using System;
using System.Diagnostics;
using System.Text;

using i64 = System.Int64;
using u8 = System.Byte;
using u16 = System.UInt16;
using u32 = System.UInt32;
using u64 = System.UInt64;
using sqlite3_int64 = System.Int64;
using Pgno = System.UInt32;
namespace NextLine.Data.SQLite.Wrapper
{
  using DbPage = Sqlite3.PgHdr;

  internal partial class Sqlite3
  {
    /*
    ** 2004 April 6
    **
    ** The author disclaims copyright to this source code.  In place of
    ** a legal notice, here is a blessing:
    **
    **    May you do good and not evil.
    **    May you find forgiveness for yourself and forgive others.
    **    May you share freely, never taking more than you give.
    **
    ** This file implements a external (disk-based) database using BTrees.
    ** See the header comment on "btreeInt.h" for additional information.
    ** Including a description of file format and an overview of operation.
    *************************************************************************
    **  Included in SQLite3 port to C#-SQLite;  2008 Noah B Hart
    **  C#-SQLite is an independent reimplementation of the SQLite software library
    **
    **  SQLITE_SOURCE_ID: 2010-03-09 19:31:43 4ae453ea7be69018d8c16eb8dabe05617397dc4d
    **
    **  $Header: Community.CsharpSqlite/src/btree_c.cs,v 6604176a7dbe 2010/03/12 23:35:36 Noah $
    *************************************************************************
    */
    //#include "btreeInt.h"

    /*
    ** The header string that appears at the beginning of every
    ** SQLite database.
    */
    static string zMagicHeader = SQLITE_FILE_HEADER;

    /*
    ** Set this global variable to 1 to enable tracing using the TRACE
    ** macro.
    */
#if TRACE 
static bool sqlite3BtreeTrace=false;  /* True to enable tracing */
//# define TRACE(X)  if(sqlite3BtreeTrace){printf X;fflush(stdout);}
static void TRACE(string X, params object[] ap) { if (sqlite3BtreeTrace)  printf(X, ap); }
#else
    //# define TRACE(X)
    static void TRACE( string X, params object[] ap ) { }
#endif



#if !SQLITE_OMIT_SHARED_CACHE
/*
** A list of BtShared objects that are eligible for participation
** in shared cache.  This variable has file scope during normal builds,
** but the test harness needs to access it so we make it global for
** test builds.
**
** Access to this variable is protected by SQLITE_MUTEX_STATIC_MASTER.
*/
#if SQLITE_TEST
BtShared *SQLITE_WSD sqlite3SharedCacheList = 0;
#else
static BtShared *SQLITE_WSD sqlite3SharedCacheList = 0;
#endif
#endif //* SQLITE_OMIT_SHARED_CACHE */

#if !SQLITE_OMIT_SHARED_CACHE
/*
** Enable or disable the shared pager and schema features.
**
** This routine has no effect on existing database connections.
** The shared cache setting effects only future calls to
** sqlite3_open(), sqlite3_open16(), or sqlite3_open_v2().
*/
int sqlite3_enable_shared_cache(int enable){
sqlite3GlobalConfig.sharedCacheEnabled = enable;
return SQLITE_OK;
}
#endif



#if SQLITE_OMIT_SHARED_CACHE
    /*
** The functions querySharedCacheTableLock(), setSharedCacheTableLock(),
** and clearAllSharedCacheTableLocks()
** manipulate entries in the BtShared.pLock linked list used to store
** shared-cache table level locks. If the library is compiled with the
** shared-cache feature disabled, then there is only ever one user
** of each BtShared structure and so this locking is not necessary.
** So define the lock related functions as no-ops.
*/
    //#define querySharedCacheTableLock(a,b,c) SQLITE_OK
    static int querySharedCacheTableLock( Btree p, Pgno iTab, u8 eLock ) { return SQLITE_OK; }

    //#define setSharedCacheTableLock(a,b,c) SQLITE_OK
    //#define clearAllSharedCacheTableLocks(a)
    static void clearAllSharedCacheTableLocks( Btree a ) { }
    //#define downgradeAllSharedCacheTableLocks(a)
    static void downgradeAllSharedCacheTableLocks( Btree a ) { }
    //#define hasSharedCacheTableLock(a,b,c,d) 1
    static bool hasSharedCacheTableLock( Btree a, Pgno b, int c, int d ) { return true; }
    //#define hasReadConflicts(a, b) 0
    static bool hasReadConflicts( Btree a, Pgno b ) { return false; }
#endif

#if !SQLITE_OMIT_SHARED_CACHE

#if SQLITE_DEBUG
/*
**** This function is only used as part of an assert() statement. ***
**
** Check to see if pBtree holds the required locks to read or write to the 
** table with root page iRoot.   Return 1 if it does and 0 if not.
**
** For example, when writing to a table with root-page iRoot via 
** Btree connection pBtree:
**
**    assert( hasSharedCacheTableLock(pBtree, iRoot, 0, WRITE_LOCK) );
**
** When writing to an index that resides in a sharable database, the 
** caller should have first obtained a lock specifying the root page of
** the corresponding table. This makes things a bit more complicated,
** as this module treats each table as a separate structure. To determine
** the table corresponding to the index being written, this
** function has to search through the database schema.
**
** Instead of a lock on the table/index rooted at page iRoot, the caller may
** hold a write-lock on the schema table (root page 1). This is also
** acceptable.
*/
static int hasSharedCacheTableLock(
Btree pBtree,         /* Handle that must hold lock */
Pgno iRoot,            /* Root page of b-tree */
int isIndex,           /* True if iRoot is the root of an index b-tree */
int eLockType          /* Required lock type (READ_LOCK or WRITE_LOCK) */
){
Schema pSchema = (Schema *)pBtree.pBt.pSchema;
Pgno iTab = 0;
BtLock pLock;

  /* If this database is not shareable, or if the client is reading
  ** and has the read-uncommitted flag set, then no lock is required. 
  ** Return true immediately.
  */
if( (pBtree.sharable==null)
|| (eLockType==READ_LOCK && (pBtree.db.flags & SQLITE_ReadUncommitted))
){
return 1;
}

  /* If the client is reading  or writing an index and the schema is
  ** not loaded, then it is too difficult to actually check to see if
  ** the correct locks are held.  So do not bother - just return true.
  ** This case does not come up very often anyhow.
  */
  if( isIndex && (!pSchema || (pSchema->flags&DB_SchemaLoaded)==0) ){
    return 1;
  }

/* Figure out the root-page that the lock should be held on. For table
** b-trees, this is just the root page of the b-tree being read or
** written. For index b-trees, it is the root page of the associated
** table.  */
if( isIndex ){
HashElem p;
for(p=sqliteHashFirst(pSchema.idxHash); p!=null; p=sqliteHashNext(p)){
Index pIdx = (Index *)sqliteHashData(p);
if( pIdx.tnum==(int)iRoot ){
iTab = pIdx.pTable.tnum;
}
}
}else{
iTab = iRoot;
}

/* Search for the required lock. Either a write-lock on root-page iTab, a
** write-lock on the schema table, or (if the client is reading) a
** read-lock on iTab will suffice. Return 1 if any of these are found.  */
for(pLock=pBtree.pBt.pLock; pLock; pLock=pLock.pNext){
if( pLock.pBtree==pBtree
&& (pLock.iTable==iTab || (pLock.eLock==WRITE_LOCK && pLock.iTable==1))
&& pLock.eLock>=eLockType
){
return 1;
}
}

/* Failed to find the required lock. */
return 0;
}

#endif //* SQLITE_DEBUG */

#if SQLITE_DEBUG
/*
** This function may be used as part of assert() statements only. ****
**
** Return true if it would be illegal for pBtree to write into the
** table or index rooted at iRoot because other shared connections are
** simultaneously reading that same table or index.
**
** It is illegal for pBtree to write if some other Btree object that
** shares the same BtShared object is currently reading or writing
** the iRoot table.  Except, if the other Btree object has the
** read-uncommitted flag set, then it is OK for the other object to
** have a read cursor.
**
** For example, before writing to any part of the table or index
** rooted at page iRoot, one should call:
**
**    assert( !hasReadConflicts(pBtree, iRoot) );
*/
static int hasReadConflicts(Btree pBtree, Pgno iRoot){
BtCursor p;
for(p=pBtree.pBt.pCursor; p!=null; p=p.pNext){
if( p.pgnoRoot==iRoot
&& p.pBtree!=pBtree
&& 0==(p.pBtree.db.flags & SQLITE_ReadUncommitted)
){
return 1;
}
}
return 0;
}
#endif    //* #if SQLITE_DEBUG */

/*
** Query to see if Btree handle p may obtain a lock of type eLock
** (READ_LOCK or WRITE_LOCK) on the table with root-page iTab. Return
** SQLITE_OK if the lock may be obtained (by calling
** setSharedCacheTableLock()), or SQLITE_LOCKED if not.
*/
static int querySharedCacheTableLock(Btree p, Pgno iTab, u8 eLock){
BtShared pBt = p.pBt;
BtLock pIter;

Debug.Assert( sqlite3BtreeHoldsMutex(p) );
Debug.Assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
Debug.Assert( p.db!=null );
Debug.Assert( !(p.db.flags&SQLITE_ReadUncommitted)||eLock==WRITE_LOCK||iTab==1 );

/* If requesting a write-lock, then the Btree must have an open write
** transaction on this file. And, obviously, for this to be so there
** must be an open write transaction on the file itself.
*/
Debug.Assert( eLock==READ_LOCK || (p==pBt.pWriter && p.inTrans==TRANS_WRITE) );
Debug.Assert( eLock==READ_LOCK || pBt.inTransaction==TRANS_WRITE );

/* This routine is a no-op if the shared-cache is not enabled */
if( !p.sharable ){
return SQLITE_OK;
}

/* If some other connection is holding an exclusive lock, the
** requested lock may not be obtained.
*/
if( pBt.pWriter!=p && pBt.isExclusive ){
sqlite3ConnectionBlocked(p.db, pBt.pWriter.db);
return SQLITE_LOCKED_SHAREDCACHE;
}

for(pIter=pBt.pLock; pIter; pIter=pIter.pNext){
/* The condition (pIter.eLock!=eLock) in the following if(...)
** statement is a simplification of:
**
**   (eLock==WRITE_LOCK || pIter.eLock==WRITE_LOCK)
**
** since we know that if eLock==WRITE_LOCK, then no other connection
** may hold a WRITE_LOCK on any table in this file (since there can
** only be a single writer).
*/
Debug.Assert( pIter.eLock==READ_LOCK || pIter.eLock==WRITE_LOCK );
Debug.Assert( eLock==READ_LOCK || pIter.pBtree==p || pIter.eLock==READ_LOCK);
if( pIter.pBtree!=p && pIter.iTable==iTab && pIter.eLock!=eLock ){
sqlite3ConnectionBlocked(p.db, pIter.pBtree.db);
if( eLock==WRITE_LOCK ){
Debug.Assert( p==pBt.pWriter );
pBt.isPending = 1;
}
return SQLITE_LOCKED_SHAREDCACHE;
}
}
return SQLITE_OK;
}
#endif //* !SQLITE_OMIT_SHARED_CACHE */

#if !SQLITE_OMIT_SHARED_CACHE
/*
** Add a lock on the table with root-page iTable to the shared-btree used
** by Btree handle p. Parameter eLock must be either READ_LOCK or 
** WRITE_LOCK.
**
** This function assumes the following:
**
**   (a) The specified Btree object p is connected to a sharable
**       database (one with the BtShared.sharable flag set), and
**
**   (b) No other Btree objects hold a lock that conflicts
**       with the requested lock (i.e. querySharedCacheTableLock() has
**       already been called and returned SQLITE_OK).
**
** SQLITE_OK is returned if the lock is added successfully. SQLITE_NOMEM 
** is returned if a malloc attempt fails.
*/
static int setSharedCacheTableLock(Btree p, Pgno iTable, u8 eLock){
BtShared pBt = p.pBt;
BtLock pLock = 0;
BtLock pIter;

Debug.Assert( sqlite3BtreeHoldsMutex(p) );
Debug.Assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
Debug.Assert( p.db!=null );

/* A connection with the read-uncommitted flag set will never try to
** obtain a read-lock using this function. The only read-lock obtained
** by a connection in read-uncommitted mode is on the sqlite_master
** table, and that lock is obtained in BtreeBeginTrans().  */
Debug.Assert( 0==(p.db.flags&SQLITE_ReadUncommitted) || eLock==WRITE_LOCK );

/* This function should only be called on a sharable b-tree after it
** has been determined that no other b-tree holds a conflicting lock.  */
Debug.Assert( p.sharable );
Debug.Assert( SQLITE_OK==querySharedCacheTableLock(p, iTable, eLock) );

/* First search the list for an existing lock on this table. */
for(pIter=pBt.pLock; pIter; pIter=pIter.pNext){
if( pIter.iTable==iTable && pIter.pBtree==p ){
pLock = pIter;
break;
}
}

/* If the above search did not find a BtLock struct associating Btree p
** with table iTable, allocate one and link it into the list.
*/
if( !pLock ){
pLock = (BtLock *)sqlite3MallocZero(sizeof(BtLock));
if( !pLock ){
return SQLITE_NOMEM;
}
pLock.iTable = iTable;
pLock.pBtree = p;
pLock.pNext = pBt.pLock;
pBt.pLock = pLock;
}

/* Set the BtLock.eLock variable to the maximum of the current lock
** and the requested lock. This means if a write-lock was already held
** and a read-lock requested, we don't incorrectly downgrade the lock.
*/
Debug.Assert( WRITE_LOCK>READ_LOCK );
if( eLock>pLock.eLock ){
pLock.eLock = eLock;
}

return SQLITE_OK;
}
#endif //* !SQLITE_OMIT_SHARED_CACHE */

#if !SQLITE_OMIT_SHARED_CACHE
/*
** Release all the table locks (locks obtained via calls to
** the setSharedCacheTableLock() procedure) held by Btree object p.
**
** This function assumes that Btree p has an open read or write 
** transaction. If it does not, then the BtShared.isPending variable
** may be incorrectly cleared.
*/
static void clearAllSharedCacheTableLocks(Btree p){
BtShared pBt = p.pBt;
BtLock **ppIter = &pBt.pLock;

Debug.Assert( sqlite3BtreeHoldsMutex(p) );
Debug.Assert( p.sharable || 0==*ppIter );
Debug.Assert( p.inTrans>0 );

while( ppIter ){
BtLock pLock = ppIter;
Debug.Assert( pBt.isExclusive==null || pBt.pWriter==pLock.pBtree );
Debug.Assert( pLock.pBtree.inTrans>=pLock.eLock );
if( pLock.pBtree==p ){
ppIter = pLock.pNext;
Debug.Assert( pLock.iTable!=1 || pLock==&p.lock );
if( pLock.iTable!=1 ){
pLock=null;//sqlite3_free(ref pLock);
}
}else{
ppIter = &pLock.pNext;
}
}

Debug.Assert( pBt.isPending==null || pBt.pWriter );
if( pBt.pWriter==p ){
pBt.pWriter = 0;
pBt.isExclusive = 0;
pBt.isPending = 0;
}else if( pBt.nTransaction==2 ){
/* This function is called when Btree p is concluding its 
** transaction. If there currently exists a writer, and p is not
** that writer, then the number of locks held by connections other
** than the writer must be about to drop to zero. In this case
** set the isPending flag to 0.
**
** If there is not currently a writer, then BtShared.isPending must
** be zero already. So this next line is harmless in that case.
*/
pBt.isPending = 0;
}
}

/*
** This function changes all write-locks held by Btree p into read-locks.
*/
static void downgradeAllSharedCacheTableLocks(Btree p){
BtShared pBt = p.pBt;
if( pBt.pWriter==p ){
BtLock pLock;
pBt.pWriter = 0;
pBt.isExclusive = 0;
pBt.isPending = 0;
for(pLock=pBt.pLock; pLock; pLock=pLock.pNext){
Debug.Assert( pLock.eLock==READ_LOCK || pLock.pBtree==p );
pLock.eLock = READ_LOCK;
}
}
}

#endif //* SQLITE_OMIT_SHARED_CACHE */

    //static void releasePage(MemPage pPage);  /* Forward reference */

    /*
    ***** This routine is used inside of assert() only ****
    **
    ** Verify that the cursor holds the mutex on its BtShared
    */
#if SQLITE_DEBUG
    static bool cursorHoldsMutex( BtCursor p )
    {
      return sqlite3_mutex_held( p.pBt.mutex );
    }
#else
static bool cursorHoldsMutex(BtCursor p) { return true; }
#endif


#if !SQLITE_OMIT_INCRBLOB
/*
** Invalidate the overflow page-list cache for cursor pCur, if any.
*/
static void invalidateOverflowCache(BtCursor pCur){
Debug.Assert( cursorHoldsMutex(pCur) );
//sqlite3_free(ref pCur.aOverflow);
pCur.aOverflow = null;
}

/*
** Invalidate the overflow page-list cache for all cursors opened
** on the shared btree structure pBt.
*/
static void invalidateAllOverflowCache(BtShared pBt){
BtCursor p;
Debug.Assert( sqlite3_mutex_held(pBt.mutex) );
for(p=pBt.pCursor; p!=null; p=p.pNext){
invalidateOverflowCache(p);
}
}

/*
** This function is called before modifying the contents of a table
** to invalidate any incrblob cursors that are open on the
** row or one of the rows being modified.
**
** If argument isClearTable is true, then the entire contents of the
** table is about to be deleted. In this case invalidate all incrblob
** cursors open on any row within the table with root-page pgnoRoot.
**
** Otherwise, if argument isClearTable is false, then the row with
** rowid iRow is being replaced or deleted. In this case invalidate
** only those incrblob cursors open on that specific row.
*/
static void invalidateIncrblobCursors(
Btree pBtree,          /* The database file to check */
i64 iRow,               /* The rowid that might be changing */
int isClearTable        /* True if all rows are being deleted */
){
BtCursor p;
BtShared pBt = pBtree.pBt;
Debug.Assert( sqlite3BtreeHoldsMutex(pBtree) );
for(p=pBt.pCursor; p!=null; p=p.pNext){
if( p.isIncrblobHandle && (isClearTable || p.info.nKey==iRow) ){
p.eState = CURSOR_INVALID;
}
}
}

#else
    /* Stub functions when INCRBLOB is omitted */
    //#define invalidateOverflowCache(x)
    static void invalidateOverflowCache( BtCursor pCur ) { }
    //#define invalidateAllOverflowCache(x)
    static void invalidateAllOverflowCache( BtShared pBt ) { }
    //#define invalidateIncrblobCursors(x,y,z)
    static void invalidateIncrblobCursors( Btree x, i64 y, int z ) { }
#endif //* SQLITE_OMIT_INCRBLOB */

    /*
** Set bit pgno of the BtShared.pHasContent bitvec. This is called
** when a page that previously contained data becomes a free-list leaf
** page.
**
** The BtShared.pHasContent bitvec exists to work around an obscure
** bug caused by the interaction of two useful IO optimizations surrounding
** free-list leaf pages:
**
**   1) When all data is deleted from a page and the page becomes
**      a free-list leaf page, the page is not written to the database
**      (as free-list leaf pages contain no meaningful data). Sometimes
**      such a page is not even journalled (as it will not be modified,
**      why bother journalling it?).
**
**   2) When a free-list leaf page is reused, its content is not read
**      from the database or written to the journal file (why should it
**      be, if it is not at all meaningful?).
**
** By themselves, these optimizations work fine and provide a handy
** performance boost to bulk delete or insert operations. However, if
** a page is moved to the free-list and then reused within the same
** transaction, a problem comes up. If the page is not journalled when
** it is moved to the free-list and it is also not journalled when it
** is extracted from the free-list and reused, then the original data
** may be lost. In the event of a rollback, it may not be possible
** to restore the database to its original configuration.
**
** The solution is the BtShared.pHasContent bitvec. Whenever a page is
** moved to become a free-list leaf page, the corresponding bit is
** set in the bitvec. Whenever a leaf page is extracted from the free-list,
** optimization 2 above is omitted if the corresponding bit is already
** set in BtShared.pHasContent. The contents of the bitvec are cleared
** at the end of every transaction.
*/
    static int btreeSetHasContent( BtShared pBt, Pgno pgno )
    {
      int rc = SQLITE_OK;
      if ( null == pBt.pHasContent )
      {
        int nPage = 100;
        sqlite3PagerPagecount( pBt.pPager, ref nPage );
        /* If sqlite3PagerPagecount() fails there is no harm because the
        ** nPage variable is unchanged from its default value of 100 */
        pBt.pHasContent = sqlite3BitvecCreate( (u32)nPage );
        if ( null == pBt.pHasContent )
        {
          rc = SQLITE_NOMEM;
        }
      }
      if ( rc == SQLITE_OK && pgno <= sqlite3BitvecSize( pBt.pHasContent ) )
      {
        rc = sqlite3BitvecSet( pBt.pHasContent, pgno );
      }
      return rc;
    }

    /*
    ** Query the BtShared.pHasContent vector.
    **
    ** This function is called when a free-list leaf page is removed from the
    ** free-list for reuse. It returns false if it is safe to retrieve the
    ** page from the pager layer with the 'no-content' flag set. True otherwise.
    */
    static bool btreeGetHasContent( BtShared pBt, Pgno pgno )
    {
      Bitvec p = pBt.pHasContent;
      return ( p != null && ( pgno > sqlite3BitvecSize( p ) || sqlite3BitvecTest( p, pgno ) != 0 ) );
    }

    /*
    ** Clear (destroy) the BtShared.pHasContent bitvec. This should be
    ** invoked at the conclusion of each write-transaction.
    */
    static void btreeClearHasContent( BtShared pBt )
    {
      sqlite3BitvecDestroy( ref pBt.pHasContent );
      pBt.pHasContent = null;
    }

    /*
    ** Save the current cursor position in the variables BtCursor.nKey
    ** and BtCursor.pKey. The cursor's state is set to CURSOR_REQUIRESEEK.
    **
    ** The caller must ensure that the cursor is valid (has eState==CURSOR_VALID)
    ** prior to calling this routine.
    */
    static int saveCursorPosition( BtCursor pCur )
    {
      int rc;

      Debug.Assert( CURSOR_VALID == pCur.eState );
      Debug.Assert( null == pCur.pKey );
      Debug.Assert( cursorHoldsMutex( pCur ) );

      rc = sqlite3BtreeKeySize( pCur, ref pCur.nKey );
      Debug.Assert( rc == SQLITE_OK );  /* KeySize() cannot fail */

      /* If this is an intKey table, then the above call to BtreeKeySize()
      ** stores the integer key in pCur.nKey. In this case this value is
      ** all that is required. Otherwise, if pCur is not open on an intKey
      ** table, then malloc space for and store the pCur.nKey bytes of key
      ** data.
      */
      if ( 0 == pCur.apPage[0].intKey )
      {
        byte[] pKey = sqlite3Malloc( (int)pCur.nKey );
        //if( pKey !=null){
        rc = sqlite3BtreeKey( pCur, 0, (u32)pCur.nKey, pKey );
        if ( rc == SQLITE_OK )
        {
          pCur.pKey = pKey;
        }
        //else{
        //  sqlite3_free(ref pKey);
        //}
        //}else{
        //  rc = SQLITE_NOMEM;
        //}
      }
      Debug.Assert( 0 == pCur.apPage[0].intKey || null == pCur.pKey );

      if ( rc == SQLITE_OK )
      {
        int i;
        for ( i = 0; i <= pCur.iPage; i++ )
        {
          releasePage( pCur.apPage[i] );
          pCur.apPage[i] = null;
        }
        pCur.iPage = -1;
        pCur.eState = CURSOR_REQUIRESEEK;
      }

      invalidateOverflowCache( pCur );
      return rc;
    }

    /*
    ** Save the positions of all cursors (except pExcept) that are open on
    ** the table  with root-page iRoot. Usually, this is called just before cursor
    ** pExcept is used to modify the table (BtreeDelete() or BtreeInsert()).
    */
    static int saveAllCursors( BtShared pBt, Pgno iRoot, BtCursor pExcept )
    {
      BtCursor p;
      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      Debug.Assert( pExcept == null || pExcept.pBt == pBt );
      for ( p = pBt.pCursor; p != null; p = p.pNext )
      {
        if ( p != pExcept && ( 0 == iRoot || p.pgnoRoot == iRoot ) &&
        p.eState == CURSOR_VALID )
        {
          int rc = saveCursorPosition( p );
          if ( SQLITE_OK != rc )
          {
            return rc;
          }
        }
      }
      return SQLITE_OK;
    }

    /*
    ** Clear the current cursor position.
    */
    static void sqlite3BtreeClearCursor( BtCursor pCur )
    {
      Debug.Assert( cursorHoldsMutex( pCur ) );
      sqlite3_free(ref pCur.pKey);
      pCur.eState = CURSOR_INVALID;
    }

    /*
    ** In this version of BtreeMoveto, pKey is a packed index record
    ** such as is generated by the OP_MakeRecord opcode.  Unpack the
    ** record and then call BtreeMovetoUnpacked() to do the work.
    */
    static int btreeMoveto(
    BtCursor pCur,     /* Cursor open on the btree to be searched */
    byte[] pKey,       /* Packed key if the btree is an index */
    i64 nKey,          /* Integer key for tables.  Size of pKey for indices */
    int bias,          /* Bias search to the high end */
    ref int pRes       /* Write search results here */
    )
    {
      int rc;                    /* Status code */
      UnpackedRecord pIdxKey;   /* Unpacked index key */
      UnpackedRecord aSpace = new UnpackedRecord();//char aSpace[150]; /* Temp space for pIdxKey - to avoid a malloc */

      if ( pKey != null )
      {
        Debug.Assert( nKey == (i64)(int)nKey );
        pIdxKey = sqlite3VdbeRecordUnpack( pCur.pKeyInfo, (int)nKey, pKey,
        aSpace, 16 );//sizeof( aSpace ) );
        if ( pIdxKey == null ) return SQLITE_NOMEM;
      }
      else
      {
        pIdxKey = null;
      }
      rc = sqlite3BtreeMovetoUnpacked( pCur, pIdxKey, nKey, bias != 0 ? 1 : 0, ref pRes );

      if ( pKey != null )
      {
        sqlite3VdbeDeleteUnpackedRecord( pIdxKey );
      }
      return rc;
    }

    /*
    ** Restore the cursor to the position it was in (or as close to as possible)
    ** when saveCursorPosition() was called. Note that this call deletes the
    ** saved position info stored by saveCursorPosition(), so there can be
    ** at most one effective restoreCursorPosition() call after each
    ** saveCursorPosition().
    */
    static int btreeRestoreCursorPosition( BtCursor pCur )
    {
      int rc;
      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( pCur.eState >= CURSOR_REQUIRESEEK );
      if ( pCur.eState == CURSOR_FAULT )
      {
        return pCur.skipNext;
      }
      pCur.eState = CURSOR_INVALID;
      rc = btreeMoveto( pCur, pCur.pKey, pCur.nKey, 0, ref pCur.skipNext );
      if ( rc == SQLITE_OK )
      {
        //sqlite3_free(ref pCur.pKey);
        pCur.pKey = null;
        Debug.Assert( pCur.eState == CURSOR_VALID || pCur.eState == CURSOR_INVALID );
      }
      return rc;
    }

    //#define restoreCursorPosition(p) \
    //  (p.eState>=CURSOR_REQUIRESEEK ? \
    //         btreeRestoreCursorPosition(p) : \
    //         SQLITE_OK)
    static int restoreCursorPosition( BtCursor pCur )
    {
      if ( pCur.eState >= CURSOR_REQUIRESEEK )
        return btreeRestoreCursorPosition( pCur );
      else
        return SQLITE_OK;
    }

    /*
    ** Determine whether or not a cursor has moved from the position it
    ** was last placed at.  Cursors can move when the row they are pointing
    ** at is deleted out from under them.
    **
    ** This routine returns an error code if something goes wrong.  The
    ** integer pHasMoved is set to one if the cursor has moved and 0 if not.
    */
    static int sqlite3BtreeCursorHasMoved( BtCursor pCur, ref int pHasMoved )
    {
      int rc;

      rc = restoreCursorPosition( pCur );
      if ( rc != 0 )
      {
        pHasMoved = 1;
        return rc;
      }
      if ( pCur.eState != CURSOR_VALID || pCur.skipNext != 0 )
      {
        pHasMoved = 1;
      }
      else
      {
        pHasMoved = 0;
      }
      return SQLITE_OK;
    }

#if !SQLITE_OMIT_AUTOVACUUM
    /*
** Given a page number of a regular database page, return the page
** number for the pointer-map page that contains the entry for the
** input page number.
*/
    static Pgno ptrmapPageno( BtShared pBt, Pgno pgno )
    {
      int nPagesPerMapPage;
      Pgno iPtrMap, ret;
      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      nPagesPerMapPage = ( pBt.usableSize / 5 ) + 1;
      iPtrMap = (Pgno)( ( pgno - 2 ) / nPagesPerMapPage );
      ret = (Pgno)( iPtrMap * nPagesPerMapPage ) + 2;
      if ( ret == PENDING_BYTE_PAGE( pBt ) )
      {
        ret++;
      }
      return ret;
    }

    /*
    ** Write an entry into the pointer map.
    **
    ** This routine updates the pointer map entry for page number 'key'
    ** so that it maps to type 'eType' and parent page number 'pgno'.
    **
    ** If pRC is initially non-zero (non-SQLITE_OK) then this routine is
    ** a no-op.  If an error occurs, the appropriate error code is written
    ** into pRC.
    */
    static void ptrmapPut( BtShared pBt, Pgno key, u8 eType, Pgno parent, ref int pRC )
    {
      DbPage pDbPage = new PgHdr(); /* The pointer map page */
      u8[] pPtrmap;                 /* The pointer map data */
      Pgno iPtrmap;                 /* The pointer map page number */
      int offset;                   /* Offset in pointer map page */
      int rc;                       /* Return code from subfunctions */

      if ( pRC != 0 ) return;

      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      /* The master-journal page number must never be used as a pointer map page */
      Debug.Assert( false == PTRMAP_ISPAGE( pBt, PENDING_BYTE_PAGE( pBt ) ) );

      Debug.Assert( pBt.autoVacuum );
      if ( key == 0 )
      {
        pRC = SQLITE_CORRUPT_BKPT();
        return;
      }
      iPtrmap = PTRMAP_PAGENO( pBt, key );
      rc = sqlite3PagerGet( pBt.pPager, iPtrmap, ref pDbPage );
      if ( rc != SQLITE_OK )
      {
        pRC = rc;
        return;
      }
      offset = (int)PTRMAP_PTROFFSET( iPtrmap, key );
      if ( offset < 0 )
      {
        pRC = SQLITE_CORRUPT_BKPT();
        goto ptrmap_exit;
      }
      pPtrmap = sqlite3PagerGetData( pDbPage );

      if ( eType != pPtrmap[offset] || sqlite3Get4byte( pPtrmap, offset + 1 ) != parent )
      {
        TRACE( "PTRMAP_UPDATE: %d->(%d,%d)\n", key, eType, parent );
        pRC = rc = sqlite3PagerWrite( pDbPage );
        if ( rc == SQLITE_OK )
        {
          pPtrmap[offset] = eType;
          sqlite3Put4byte( pPtrmap, offset + 1, parent );
        }
      }

    ptrmap_exit:
      sqlite3PagerUnref( pDbPage );
    }

    /*
    ** Read an entry from the pointer map.
    **
    ** This routine retrieves the pointer map entry for page 'key', writing
    ** the type and parent page number to pEType and pPgno respectively.
    ** An error code is returned if something goes wrong, otherwise SQLITE_OK.
    */
    static int ptrmapGet( BtShared pBt, Pgno key, ref u8 pEType, ref Pgno pPgno )
    {
      DbPage pDbPage = new PgHdr();/* The pointer map page */
      int iPtrmap;                 /* Pointer map page index */
      u8[] pPtrmap;                /* Pointer map page data */
      int offset;                  /* Offset of entry in pointer map */
      int rc;

      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );

      iPtrmap = (int)PTRMAP_PAGENO( pBt, key );
      rc = sqlite3PagerGet( pBt.pPager, (u32)iPtrmap, ref pDbPage );
      if ( rc != 0 )
      {
        return rc;
      }
      pPtrmap = sqlite3PagerGetData( pDbPage );

      offset = (int)PTRMAP_PTROFFSET( (u32)iPtrmap, key );
      // Under C# pEType will always exist. No need to test; //
      //Debug.Assert( pEType != 0 );
      pEType = pPtrmap[offset];
      // Under C# pPgno will always exist. No need to test; //
      //if ( pPgno != 0 )
      pPgno = sqlite3Get4byte( pPtrmap, offset + 1 );

      sqlite3PagerUnref( pDbPage );
      if ( pEType < 1 || pEType > 5 )
        return SQLITE_CORRUPT_BKPT();
      return SQLITE_OK;
    }

#else //* if defined SQLITE_OMIT_AUTOVACUUM */
//#define ptrmapPut(w,x,y,z,rc)
//#define ptrmapGet(w,x,y,z) SQLITE_OK
//#define ptrmapPutOvflPtr(x, y, rc)
#endif

    /*
** Given a btree page and a cell index (0 means the first cell on
** the page, 1 means the second cell, and so forth) return a pointer
** to the cell content.
**
** This routine works only for pages that do not contain overflow cells.
*/
    //#define findCell(P,I) \
    //  ((P).aData + ((P).maskPage & get2byte((P).aData[(P).cellOffset+2*(I)])))
    static int findCell( MemPage pPage, int iCell )
    {
      return get2byte( pPage.aData, pPage.cellOffset + 2 * ( iCell ) );
    }
    /*
    ** This a more complex version of findCell() that works for
    ** pages that do contain overflow cells.
    */
    static int findOverflowCell( MemPage pPage, int iCell )
    {
      int i;
      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      for ( i = pPage.nOverflow - 1; i >= 0; i-- )
      {
        int k;
        _OvflCell pOvfl;
        pOvfl = pPage.aOvfl[i];
        k = pOvfl.idx;
        if ( k <= iCell )
        {
          if ( k == iCell )
          {
            //return pOvfl.pCell;
            return -i - 1; // Negative Offset means overflow cells
          }
          iCell--;
        }
      }
      return findCell( pPage, iCell );
    }

    /*
    ** Parse a cell content block and fill in the CellInfo structure.  There
    ** are two versions of this function.  btreeParseCell() takes a
    ** cell index as the second argument and btreeParseCellPtr()
    ** takes a pointer to the body of the cell as its second argument.
    **
    ** Within this file, the parseCell() macro can be called instead of
    ** btreeParseCellPtr(). Using some compilers, this will be faster.
    */
    //OVERLOADS
    static void btreeParseCellPtr(
    MemPage pPage,        /* Page containing the cell */
    int iCell,            /* Pointer to the cell text. */
    ref CellInfo pInfo    /* Fill in this structure */
    )
    { btreeParseCellPtr( pPage, pPage.aData, iCell, ref pInfo ); }
    static void btreeParseCellPtr(
    MemPage pPage,        /* Page containing the cell */
    byte[] pCell,         /* The actual data */
    ref CellInfo pInfo    /* Fill in this structure */
    )
    { btreeParseCellPtr( pPage, pCell, 0, ref pInfo ); }
    static void btreeParseCellPtr(
    MemPage pPage,         /* Page containing the cell */
    u8[] pCell,            /* Pointer to the cell text. */
    int iCell,             /* Pointer to the cell text. */
    ref CellInfo pInfo     /* Fill in this structure */
    )
    {
      u16 n;               /* Number bytes in cell content header */
      u32 nPayload = 0;    /* Number of bytes of cell payload */

      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );

      if (pInfo.pCell != pCell) pInfo.pCell = pCell;
      pInfo.iCell = iCell;
      Debug.Assert( pPage.leaf == 0 || pPage.leaf == 1 );
      n = pPage.childPtrSize;
      Debug.Assert( n == 4 - 4 * pPage.leaf );
      if ( pPage.intKey != 0 )
      {
        if ( pPage.hasData != 0 )
        {
          n += (u16)getVarint32( pCell, iCell + n, ref nPayload );
        }
        else
        {
          nPayload = 0;
        }
        n += (u16)getVarint( pCell, iCell + n, ref pInfo.nKey );
        pInfo.nData = nPayload;
      }
      else
      {
        pInfo.nData = 0;
        n += (u16)getVarint32( pCell, iCell + n, ref nPayload );
        pInfo.nKey = nPayload;
      }
      pInfo.nPayload = nPayload;
      pInfo.nHeader = n;
      testcase( nPayload == pPage.maxLocal );
      testcase( nPayload == pPage.maxLocal + 1 );
      if ( likely( nPayload <= pPage.maxLocal ) )
      {
        /* This is the (easy) common case where the entire payload fits
        ** on the local page.  No overflow is required.
        */
        int nSize;          /* Total size of cell content in bytes */
        nSize = (int)nPayload + n;
        pInfo.nLocal = (u16)nPayload;
        pInfo.iOverflow = 0;
        if ( ( nSize & ~3 ) == 0 )
        {
          nSize = 4;        /* Minimum cell size is 4 */
        }
        pInfo.nSize = (u16)nSize;
      }
      else
      {
        /* If the payload will not fit completely on the local page, we have
        ** to decide how much to store locally and how much to spill onto
        ** overflow pages.  The strategy is to minimize the amount of unused
        ** space on overflow pages while keeping the amount of local storage
        ** in between minLocal and maxLocal.
        **
        ** Warning:  changing the way overflow payload is distributed in any
        ** way will result in an incompatible file format.
        */
        int minLocal;  /* Minimum amount of payload held locally */
        int maxLocal;  /* Maximum amount of payload held locally */
        int surplus;   /* Overflow payload available for local storage */

        minLocal = pPage.minLocal;
        maxLocal = pPage.maxLocal;
        surplus = (int)( minLocal + ( nPayload - minLocal ) % ( pPage.pBt.usableSize - 4 ) );
        testcase( surplus == maxLocal );
        testcase( surplus == maxLocal + 1 );
        if ( surplus <= maxLocal )
        {
          pInfo.nLocal = (u16)surplus;
        }
        else
        {
          pInfo.nLocal = (u16)minLocal;
        }
        pInfo.iOverflow = (u16)( pInfo.nLocal + n );
        pInfo.nSize = (u16)( pInfo.iOverflow + 4 );
      }
    }
    //#define parseCell(pPage, iCell, pInfo) \
    //  btreeParseCellPtr((pPage), findCell((pPage), (iCell)), (pInfo))
    static void parseCell( MemPage pPage, int iCell, ref CellInfo pInfo )
    {
      btreeParseCellPtr( pPage, findCell(pPage, iCell ), ref  pInfo  );
    }

    static void btreeParseCell(
    MemPage pPage,         /* Page containing the cell */
    int iCell,              /* The cell index.  First cell is 0 */
    ref CellInfo pInfo         /* Fill in this structure */
    )
    {
      parseCell( pPage, iCell, ref pInfo );
    }

    /*
    ** Compute the total number of bytes that a Cell needs in the cell
    ** data area of the btree-page.  The return number includes the cell
    ** data header and the local payload, but not any overflow page or
    ** the space used by the cell pointer.
    */
    // Alternative form for C#
    static u16 cellSizePtr(MemPage pPage, int iCell)
    {
      CellInfo info = new CellInfo();
      byte[] pCell = new byte[13];
      //byte[] pCell = new byte[13];// Minimum Size = (2 bytes of Header  or (4) Child Pointer) + (maximum of) 9 bytes data
      if ( iCell < 0 )// Overflow Cell
        Buffer.BlockCopy( pPage.aOvfl[-( iCell + 1 )].pCell, 0, pCell, 0, pCell.Length < pPage.aOvfl[-( iCell + 1 )].pCell.Length ? pCell.Length : pPage.aOvfl[-( iCell + 1 )].pCell.Length );
      else if ( iCell >= pPage.aData.Length + 1 - pCell.Length )
        Buffer.BlockCopy( pPage.aData, iCell, pCell, 0, pPage.aData.Length - iCell );
      else
        Buffer.BlockCopy( pPage.aData, iCell, pCell, 0, pCell.Length );
      btreeParseCellPtr( pPage, pCell, ref info );
      return info.nSize;
    }

    // Alternative form for C#
    static u16 cellSizePtr( MemPage pPage, byte[] pCell, int offset )
    {
      CellInfo info = new CellInfo();
      info.pCell = sqlite3Malloc( pCell.Length );
      Buffer.BlockCopy( pCell, offset, info.pCell, 0, pCell.Length - offset );
      btreeParseCellPtr( pPage, info.pCell, ref info );
      return info.nSize;
    }

    static u16 cellSizePtr( MemPage pPage, u8[] pCell )
    {
      int _pIter = pPage.childPtrSize; //u8 pIter = &pCell[pPage.childPtrSize];
      u32 nSize = 0;

#if SQLITE_DEBUG || DEBUG
      /* The value returned by this function should always be the same as
** the (CellInfo.nSize) value found by doing a full parse of the
** cell. If SQLITE_DEBUG is defined, an Debug.Assert() at the bottom of
** this function verifies that this invariant is not violated. */
      CellInfo debuginfo = new CellInfo();
      btreeParseCellPtr( pPage, pCell, ref debuginfo );
#else
      CellInfo debuginfo = new CellInfo();
#endif

      if ( pPage.intKey != 0 )
      {
        int pEnd;
        if ( pPage.hasData != 0 )
        {
          _pIter += getVarint32( pCell, ref nSize );// pIter += getVarint32( pIter, ref nSize );
        }
        else
        {
          nSize = 0;
        }

        /* pIter now points at the 64-bit integer key value, a variable length
        ** integer. The following block moves pIter to point at the first byte
        ** past the end of the key value. */
        pEnd = _pIter + 9;//pEnd = &pIter[9];
        while ( ( ( pCell[_pIter++] ) & 0x80 ) != 0 && _pIter < pEnd ) ;//while( (pIter++)&0x80 && pIter<pEnd );
      }
      else
      {
        _pIter += getVarint32( pCell, _pIter, ref nSize ); //pIter += getVarint32( pIter, ref nSize );
      }

      testcase( nSize == pPage.maxLocal );
      testcase( nSize == pPage.maxLocal + 1 );
      if ( nSize > pPage.maxLocal )
      {
        int minLocal = pPage.minLocal;
        nSize = (u32)( minLocal + ( nSize - minLocal ) % ( pPage.pBt.usableSize - 4 ) );
        testcase( nSize == pPage.maxLocal );
        testcase( nSize == pPage.maxLocal + 1 );
        if ( nSize > pPage.maxLocal )
        {
          nSize = (u32)minLocal;
        }
        nSize += 4;
      }
      nSize += (uint)_pIter;//nSize += (u32)(pIter - pCell);

      /* The minimum size of any cell is 4 bytes. */
      if ( nSize < 4 )
      {
        nSize = 4;
      }

      Debug.Assert( nSize == debuginfo.nSize );
      return (u16)nSize;
    }

#if SQLITE_DEBUG
    /* This variation on cellSizePtr() is used inside of assert() statements
** only. */
    static u16 cellSize( MemPage pPage, int iCell )
    {
      return cellSizePtr( pPage, findCell( pPage, iCell ) );
    }
#else
static int cellSize(MemPage pPage, int iCell) { return -1; }
#endif

#if !SQLITE_OMIT_AUTOVACUUM
    /*
** If the cell pCell, part of page pPage contains a pointer
** to an overflow page, insert an entry into the pointer-map
** for the overflow page.
*/
    static void ptrmapPutOvflPtr( MemPage pPage, int pCell, ref int pRC )
    {
      if ( pRC != 0 ) return;
      CellInfo info = new CellInfo();
      Debug.Assert( pCell != 0 );
      btreeParseCellPtr( pPage, pCell, ref info );
      Debug.Assert( ( info.nData + ( pPage.intKey != 0 ? 0 : info.nKey ) ) == info.nPayload );
      if ( info.iOverflow != 0 )
      {
        Pgno ovfl = sqlite3Get4byte( pPage.aData, pCell, info.iOverflow );
        ptrmapPut( pPage.pBt, ovfl, PTRMAP_OVERFLOW1, pPage.pgno, ref pRC );
      }
    }

    static void ptrmapPutOvflPtr( MemPage pPage, u8[] pCell, ref int pRC )
    {
      if ( pRC != 0 ) return;
      CellInfo info = new CellInfo();
      Debug.Assert( pCell != null );
      btreeParseCellPtr( pPage, pCell, ref info );
      Debug.Assert( ( info.nData + ( pPage.intKey != 0 ? 0 : info.nKey ) ) == info.nPayload );
      if ( info.iOverflow != 0 )
      {
        Pgno ovfl = sqlite3Get4byte( pCell, info.iOverflow );
        ptrmapPut( pPage.pBt, ovfl, PTRMAP_OVERFLOW1, pPage.pgno, ref pRC );
      }
    }
#endif


    /*
** Defragment the page given.  All Cells are moved to the
** end of the page and all free space is collected into one
** big FreeBlk that occurs in between the header and cell
** pointer array and the cell content area.
*/
    static int defragmentPage( MemPage pPage )
    {
      int i;                     /* Loop counter */
      int pc;                    /* Address of a i-th cell */
      int addr;                  /* Offset of first byte after cell pointer array */
      int hdr;                   /* Offset to the page header */
      int size;                  /* Size of a cell */
      int usableSize;            /* Number of usable bytes on a page */
      int cellOffset;            /* Offset to the cell pointer array */
      int cbrk;                  /* Offset to the cell content area */
      int nCell;                 /* Number of cells on the page */
      byte[] data;               /* The page data */
      byte[] temp;               /* Temp area for cell content */
      int iCellFirst;            /* First allowable cell index */
      int iCellLast;             /* Last possible cell index */


      Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
      Debug.Assert( pPage.pBt != null );
      Debug.Assert( pPage.pBt.usableSize <= SQLITE_MAX_PAGE_SIZE );
      Debug.Assert( pPage.nOverflow == 0 );
      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      temp = sqlite3PagerTempSpace( pPage.pBt.pPager );
      data = pPage.aData;
      hdr = pPage.hdrOffset;
      cellOffset = pPage.cellOffset;
      nCell = pPage.nCell;
      Debug.Assert( nCell == get2byte( data, hdr + 3 ) );
      usableSize = pPage.pBt.usableSize;
      cbrk = get2byte( data, hdr + 5 );
      Buffer.BlockCopy( data, cbrk, temp, cbrk, usableSize - cbrk );//memcpy( temp[cbrk], ref data[cbrk], usableSize - cbrk );
      cbrk = usableSize;
      iCellFirst = cellOffset + 2 * nCell;
      iCellLast = usableSize - 4;
      for ( i = 0; i < nCell; i++ )
      {
        int pAddr;     /* The i-th cell pointer */
        pAddr = cellOffset + i * 2; // &data[cellOffset + i * 2];
        pc = get2byte( data, pAddr );
        testcase( pc == iCellFirst );
        testcase( pc == iCellLast );
#if !(SQLITE_ENABLE_OVERSIZE_CELL_CHECK)
/* These conditions have already been verified in btreeInitPage()
** if SQLITE_ENABLE_OVERSIZE_CELL_CHECK is defined
*/
if( pc<iCellFirst || pc>iCellLast ){
return SQLITE_CORRUPT_BKPT();
}
#endif
        Debug.Assert( pc >= iCellFirst && pc <= iCellLast );
        size = cellSizePtr( pPage, temp, pc );
        cbrk -= size;
#if (SQLITE_ENABLE_OVERSIZE_CELL_CHECK)
        if ( cbrk < iCellFirst )
        {
          return SQLITE_CORRUPT_BKPT();
        }
#else
if( cbrk<iCellFirst || pc+size>usableSize ){
return SQLITE_CORRUPT_BKPT();
}
#endif
        Debug.Assert( cbrk + size <= usableSize && cbrk >= iCellFirst );
        testcase( cbrk + size == usableSize );
        testcase( pc + size == usableSize );
        Buffer.BlockCopy( temp, pc, data, cbrk, size );//memcpy(data[cbrk], ref temp[pc], size);
        put2byte( data, pAddr, cbrk );
      }
      Debug.Assert( cbrk >= iCellFirst );
      put2byte( data, hdr + 5, cbrk );
      data[hdr + 1] = 0;
      data[hdr + 2] = 0;
      data[hdr + 7] = 0;
      addr = cellOffset + 2 * nCell;
      Array.Clear( data, addr, cbrk - addr );  //memset(data[iCellFirst], 0, cbrk-iCellFirst);
      Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
      if ( cbrk - iCellFirst != pPage.nFree )
      {
        return SQLITE_CORRUPT_BKPT();
      }
      return SQLITE_OK;
    }

    /*
    ** Allocate nByte bytes of space from within the B-Tree page passed
    ** as the first argument. Write into pIdx the index into pPage.aData[]
    ** of the first byte of allocated space. Return either SQLITE_OK or
    ** an error code (usually SQLITE_CORRUPT).
    **
    ** The caller guarantees that there is sufficient space to make the
    ** allocation.  This routine might need to defragment in order to bring
    ** all the space together, however.  This routine will avoid using
    ** the first two bytes past the cell pointer area since presumably this
    ** allocation is being made in order to insert a new cell, so we will
    ** also end up needing a new cell pointer.
    */
    static int allocateSpace( MemPage pPage, int nByte, ref int pIdx )
    {
      int hdr = pPage.hdrOffset;  /* Local cache of pPage.hdrOffset */
      u8[] data = pPage.aData;    /* Local cache of pPage.aData */
      int nFrag;                  /* Number of fragmented bytes on pPage */
      int top;                    /* First byte of cell content area */
      int gap;                    /* First byte of gap between cell pointers and cell content */
      int rc;                     /* Integer return code */
      int usableSize;             /* Usable size of the page */

      Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
      Debug.Assert( pPage.pBt != null );
      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      Debug.Assert( nByte >= 0 );  /* Minimum cell size is 4 */
      Debug.Assert( pPage.nFree >= nByte );
      Debug.Assert( pPage.nOverflow == 0 );
      usableSize = pPage.pBt.usableSize;
      Debug.Assert( nByte < usableSize - 8 );

      nFrag = data[hdr + 7];
      Debug.Assert( pPage.cellOffset == hdr + 12 - 4 * pPage.leaf );
      gap = pPage.cellOffset + 2 * pPage.nCell;
      top = get2byte( data, hdr + 5 );
      if ( gap > top )
        return SQLITE_CORRUPT_BKPT();
      testcase( gap + 2 == top );
      testcase( gap + 1 == top );
      testcase( gap == top );

      if ( nFrag >= 60 )
      {
        /* Always defragment highly fragmented pages */
        rc = defragmentPage( pPage );
        if ( rc != 0 ) return rc;
        top = get2byte( data, hdr + 5 );
      }
      else if ( gap + 2 <= top )
      {
        /* Search the freelist looking for a free slot big enough to satisfy
        ** the request. The allocation is made from the first free slot in
        ** the list that is large enough to accomadate it.
        */
        int pc, addr;
        for ( addr = hdr + 1; ( pc = get2byte( data, addr ) ) > 0; addr = pc )
        {
          int size;     /* Size of free slot */
          if ( pc > usableSize - 4 || pc < addr + 4 )
          {
            return SQLITE_CORRUPT_BKPT();
          }
          size = get2byte( data, pc + 2 );
          if ( size >= nByte )
          {
            int x = size - nByte;
            testcase( x == 4 );
            testcase( x == 3 );
            if ( x < 4 )
            {
              /* Remove the slot from the free-list. Update the number of
              ** fragmented bytes within the page. */
              data[addr + 0] = data[pc + 0]; data[addr + 1] = data[pc + 1]; //memcpy( data[addr], ref data[pc], 2 );
              data[hdr + 7] = (u8)( nFrag + x );
            }
            else if ( size + pc > usableSize )
            {
              return SQLITE_CORRUPT_BKPT();
            }
            else
            {
              /* The slot remains on the free-list. Reduce its size to account
              ** for the portion used by the new allocation. */
              put2byte( data, pc + 2, x );
            }
            pIdx = pc + x;
            return SQLITE_OK;
          }
        }
      }

      /* Check to make sure there is enough space in the gap to satisfy
      ** the allocation.  If not, defragment.
      */
      testcase( gap + 2 + nByte == top );
      if ( gap + 2 + nByte > top )
      {
        rc = defragmentPage( pPage );
        if ( rc != 0 ) return rc;
        top = get2byte( data, hdr + 5 );
        Debug.Assert( gap + nByte <= top );
      }


      /* Allocate memory from the gap in between the cell pointer array
      ** and the cell content area.  The btreeInitPage() call has already
      ** validated the freelist.  Given that the freelist is valid, there
      ** is no way that the allocation can extend off the end of the page.
      ** The Debug.Assert() below verifies the previous sentence.
      */
      top -= nByte;
      put2byte( data, hdr + 5, top );
      Debug.Assert( top + nByte <= pPage.pBt.usableSize );
      pIdx = top;
      return SQLITE_OK;
    }

    /*
    ** Return a section of the pPage.aData to the freelist.
    ** The first byte of the new free block is pPage.aDisk[start]
    ** and the size of the block is "size" bytes.
    **
    ** Most of the effort here is involved in coalesing adjacent
    ** free blocks into a single big free block.
    */
    static int freeSpace( MemPage pPage, int start, int size )
    {
      int addr, pbegin, hdr;
      int iLast;                        /* Largest possible freeblock offset */
      byte[] data = pPage.aData;

      Debug.Assert( pPage.pBt != null );
      Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
      Debug.Assert( start >= pPage.hdrOffset + 6 + pPage.childPtrSize );
      Debug.Assert( ( start + size ) <= pPage.pBt.usableSize );
      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      Debug.Assert( size >= 0 );   /* Minimum cell size is 4 */

      if (pPage.pBt.secureDelete)
      {
        /* Overwrite deleted information with zeros when the secure_delete
        ** option is enabled */
        Array.Clear(data, start, size);// memset(&data[start], 0, size);
      }

      /* Add the space back into the linked list of freeblocks.  Note that
** even though the freeblock list was checked by btreeInitPage(),
** btreeInitPage() did not detect overlapping cells or
** freeblocks that overlapped cells.   Nor does it detect when the
** cell content area exceeds the value in the page header.  If these
** situations arise, then subsequent insert operations might corrupt
** the freelist.  So we do need to check for corruption while scanning
** the freelist.
*/
      hdr = pPage.hdrOffset;
      addr = hdr + 1;
      iLast = pPage.pBt.usableSize - 4;
      Debug.Assert( start <= iLast );
      while ( ( pbegin = get2byte( data, addr ) ) < start && pbegin > 0 )
      {
        if ( pbegin < addr + 4 )
        {
          return SQLITE_CORRUPT_BKPT();
        }
        addr = pbegin;
      }
      if ( pbegin > iLast )
      {
        return SQLITE_CORRUPT_BKPT();
      }
      Debug.Assert( pbegin > addr || pbegin == 0 );
      put2byte( data, addr, start );
      put2byte( data, start, pbegin );
      put2byte( data, start + 2, size );
      pPage.nFree = (u16)( pPage.nFree + size );

      /* Coalesce adjacent free blocks */
      addr = hdr + 1;
      while ( ( pbegin = get2byte( data, addr ) ) > 0 )
      {
        int pnext, psize, x;
        Debug.Assert( pbegin > addr );
        Debug.Assert( pbegin <= pPage.pBt.usableSize - 4 );
        pnext = get2byte( data, pbegin );
        psize = get2byte( data, pbegin + 2 );
        if ( pbegin + psize + 3 >= pnext && pnext > 0 )
        {
          int frag = pnext - ( pbegin + psize );
          if ( ( frag < 0 ) || ( frag > (int)data[hdr + 7] ) )
          {
            return SQLITE_CORRUPT_BKPT();
          }
          data[hdr + 7] -= (u8)frag;
          x = get2byte( data, pnext );
          put2byte( data, pbegin, x );
          x = pnext + get2byte( data, pnext + 2 ) - pbegin;
          put2byte( data, pbegin + 2, x );
        }
        else
        {
          addr = pbegin;
        }
      }

      /* If the cell content area begins with a freeblock, remove it. */
      if ( data[hdr + 1] == data[hdr + 5] && data[hdr + 2] == data[hdr + 6] )
      {
        int top;
        pbegin = get2byte( data, hdr + 1 );
        put2byte( data, hdr + 1, get2byte( data, pbegin ) ); //memcpy( data[hdr + 1], ref data[pbegin], 2 );
        top = get2byte( data, hdr + 5 ) + get2byte( data, pbegin + 2 );
        put2byte( data, hdr + 5, top );
      }
      Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
      return SQLITE_OK;
    }

    /*
    ** Decode the flags byte (the first byte of the header) for a page
    ** and initialize fields of the MemPage structure accordingly.
    **
    ** Only the following combinations are supported.  Anything different
    ** indicates a corrupt database files:
    **
    **         PTF_ZERODATA
    **         PTF_ZERODATA | PTF_LEAF
    **         PTF_LEAFDATA | PTF_INTKEY
    **         PTF_LEAFDATA | PTF_INTKEY | PTF_LEAF
    */
    static int decodeFlags( MemPage pPage, int flagByte )
    {
      BtShared pBt;     /* A copy of pPage.pBt */

      Debug.Assert( pPage.hdrOffset == ( pPage.pgno == 1 ? 100 : 0 ) );
      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      pPage.leaf = (u8)( flagByte >> 3 ); Debug.Assert( PTF_LEAF == 1 << 3 );
      flagByte &= ~PTF_LEAF;
      pPage.childPtrSize = (u8)( 4 - 4 * pPage.leaf );
      pBt = pPage.pBt;
      if ( flagByte == ( PTF_LEAFDATA | PTF_INTKEY ) )
      {
        pPage.intKey = 1;
        pPage.hasData = pPage.leaf;
        pPage.maxLocal = pBt.maxLeaf;
        pPage.minLocal = pBt.minLeaf;
      }
      else if ( flagByte == PTF_ZERODATA )
      {
        pPage.intKey = 0;
        pPage.hasData = 0;
        pPage.maxLocal = pBt.maxLocal;
        pPage.minLocal = pBt.minLocal;
      }
      else
      {
        return SQLITE_CORRUPT_BKPT();
      }
      return SQLITE_OK;
    }

    /*
    ** Initialize the auxiliary information for a disk block.
    **
    ** Return SQLITE_OK on success.  If we see that the page does
    ** not contain a well-formed database page, then return
    ** SQLITE_CORRUPT.  Note that a return of SQLITE_OK does not
    ** guarantee that the page is well-formed.  It only shows that
    ** we failed to detect any corruption.
    */
    static int btreeInitPage( MemPage pPage )
    {

      Debug.Assert( pPage.pBt != null );
      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      Debug.Assert( pPage.pgno == sqlite3PagerPagenumber( pPage.pDbPage ) );
      Debug.Assert( pPage == sqlite3PagerGetExtra( pPage.pDbPage ) );
      Debug.Assert( pPage.aData == sqlite3PagerGetData( pPage.pDbPage ) );

      if ( 0 == pPage.isInit )
      {
        u16 pc;            /* Address of a freeblock within pPage.aData[] */
        u8 hdr;            /* Offset to beginning of page header */
        u8[] data;         /* Equal to pPage.aData */
        BtShared pBt;      /* The main btree structure */
        u16 usableSize;    /* Amount of usable space on each page */
        u16 cellOffset;    /* Offset from start of page to first cell pointer */
        u16 nFree;         /* Number of unused bytes on the page */
        u16 top;           /* First byte of the cell content area */
        int iCellFirst;    /* First allowable cell or freeblock offset */
        int iCellLast;     /* Last possible cell or freeblock offset */

        pBt = pPage.pBt;

        hdr = pPage.hdrOffset;
        data = pPage.aData;
        if ( decodeFlags( pPage, data[hdr] ) != 0 )
          return SQLITE_CORRUPT_BKPT();
        Debug.Assert( pBt.pageSize >= 512 && pBt.pageSize <= 32768 );
        pPage.maskPage = (u16)( pBt.pageSize - 1 );
        pPage.nOverflow = 0;
        usableSize = pBt.usableSize;
        pPage.cellOffset = ( cellOffset = (u16)( hdr + 12 - 4 * pPage.leaf ) );
        top = (u16)get2byte( data, hdr + 5 );
        pPage.nCell = (u16)( get2byte( data, hdr + 3 ) );
        if ( pPage.nCell > MX_CELL( pBt ) )
        {
          /* To many cells for a single page.  The page must be corrupt */
          return SQLITE_CORRUPT_BKPT();
        }
        testcase( pPage.nCell == MX_CELL( pBt ) );

        /* A malformed database page might cause us to read past the end
        ** of page when parsing a cell.
        **
        ** The following block of code checks early to see if a cell extends
        ** past the end of a page boundary and causes SQLITE_CORRUPT to be
        ** returned if it does.
        */
        iCellFirst = cellOffset + 2 * pPage.nCell;
        iCellLast = usableSize - 4;
#if (SQLITE_ENABLE_OVERSIZE_CELL_CHECK)
        {
          int i;            /* Index into the cell pointer array */
          int sz;           /* Size of a cell */

          if ( 0 == pPage.leaf ) iCellLast--;
          for ( i = 0; i < pPage.nCell; i++ )
          {
            pc = (u16)get2byte( data, cellOffset + i * 2 );
            testcase( pc == iCellFirst );
            testcase( pc == iCellLast );
            if ( pc < iCellFirst || pc > iCellLast )
            {
              return SQLITE_CORRUPT_BKPT();
            }
            sz = cellSizePtr( pPage, data, pc );
            testcase( pc + sz == usableSize );
            if ( pc + sz > usableSize )
            {
              return SQLITE_CORRUPT_BKPT();
            }
          }
          if ( 0 == pPage.leaf ) iCellLast++;
        }
#endif

        /* Compute the total free space on the page */
        pc = (u16)get2byte( data, hdr + 1 );
        nFree = (u16)( data[hdr + 7] + top );
        while ( pc > 0 )
        {
          u16 next, size;
          if ( pc < iCellFirst || pc > iCellLast )
          {
            /* Start of free block is off the page */
            return SQLITE_CORRUPT_BKPT();
          }
          next = (u16)get2byte( data, pc );
          size = (u16)get2byte( data, pc + 2 );
          if ( ( next > 0 && next <= pc + size + 3 ) || pc + size > usableSize )
          {
            /* Free blocks must be in ascending order. And the last byte of
      ** the free-block must lie on the database page.  */
            return SQLITE_CORRUPT_BKPT();
          }
          nFree = (u16)( nFree + size );
          pc = next;
        }

        /* At this point, nFree contains the sum of the offset to the start
        ** of the cell-content area plus the number of free bytes within
        ** the cell-content area. If this is greater than the usable-size
        ** of the page, then the page must be corrupted. This check also
        ** serves to verify that the offset to the start of the cell-content
        ** area, according to the page header, lies within the page.
        */
        if ( nFree > usableSize )
        {
          return SQLITE_CORRUPT_BKPT();
        }
        pPage.nFree = (u16)( nFree - iCellFirst );
        pPage.isInit = 1;
      }
      return SQLITE_OK;
    }

    /*
    ** Set up a raw page so that it looks like a database page holding
    ** no entries.
    */
    static void zeroPage( MemPage pPage, int flags )
    {
      byte[] data = pPage.aData;
      BtShared pBt = pPage.pBt;
      u8 hdr = pPage.hdrOffset;
      u16 first;

      Debug.Assert( sqlite3PagerPagenumber( pPage.pDbPage ) == pPage.pgno );
      Debug.Assert( sqlite3PagerGetExtra( pPage.pDbPage ) == pPage );
      Debug.Assert( sqlite3PagerGetData( pPage.pDbPage ) == data );
      Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      if (pBt.secureDelete)
      {
        Array.Clear( data, hdr, pBt.usableSize - hdr);//memset(&data[hdr], 0, pBt->usableSize - hdr);
      }

      data[hdr] = (u8)flags;
      first = (u16)( hdr + 8 + 4 * ( ( flags & PTF_LEAF ) == 0 ? 1 : 0 ) );
      Array.Clear( data, hdr + 1, 4 );//memset(data[hdr+1], 0, 4);
      data[hdr + 7] = 0;
      put2byte( data, hdr + 5, pBt.usableSize );
      pPage.nFree = (u16)( pBt.usableSize - first );
      decodeFlags( pPage, flags );
      pPage.hdrOffset = hdr;
      pPage.cellOffset = first;
      pPage.nOverflow = 0;
      Debug.Assert( pBt.pageSize >= 512 && pBt.pageSize <= 32768 );
      pPage.maskPage = (u16)( pBt.pageSize - 1 );
      pPage.nCell = 0;
      pPage.isInit = 1;
    }


    /*
    ** Convert a DbPage obtained from the pager into a MemPage used by
    ** the btree layer.
    */
    static MemPage btreePageFromDbPage( DbPage pDbPage, Pgno pgno, BtShared pBt )
    {
      MemPage pPage = (MemPage)sqlite3PagerGetExtra( pDbPage );
      pPage.aData = sqlite3PagerGetData( pDbPage );
      pPage.pDbPage = pDbPage;
      pPage.pBt = pBt;
      pPage.pgno = pgno;
      pPage.hdrOffset = (u8)( pPage.pgno == 1 ? 100 : 0 );
      return pPage;
    }

    /*
    ** Get a page from the pager.  Initialize the MemPage.pBt and
    ** MemPage.aData elements if needed.
    **
    ** If the noContent flag is set, it means that we do not care about
    ** the content of the page at this time.  So do not go to the disk
    ** to fetch the content.  Just fill in the content with zeros for now.
    ** If in the future we call sqlite3PagerWrite() on this page, that
    ** means we have started to be concerned about content and the disk
    ** read should occur at that point.
    */
    static int btreeGetPage(
    BtShared pBt,        /* The btree */
    Pgno pgno,           /* Number of the page to fetch */
    ref MemPage ppPage,  /* Return the page in this parameter */
    int noContent        /* Do not load page content if true */
    )
    {
      int rc;
      DbPage pDbPage = null;

      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      rc = sqlite3PagerAcquire( pBt.pPager, pgno, ref pDbPage, (u8)noContent );
      if ( rc != 0 ) return rc;
      ppPage = btreePageFromDbPage( pDbPage, pgno, pBt );
      return SQLITE_OK;
    }

    /*
    ** Retrieve a page from the pager cache. If the requested page is not
    ** already in the pager cache return NULL. Initialize the MemPage.pBt and
    ** MemPage.aData elements if needed.
    */
    static MemPage btreePageLookup( BtShared pBt, Pgno pgno )
    {
      DbPage pDbPage;
      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      pDbPage = sqlite3PagerLookup( pBt.pPager, pgno );
      if ( pDbPage )
      {
        return btreePageFromDbPage( pDbPage, pgno, pBt );
      }
      return null;
    }

    /*
    ** Return the size of the database file in pages. If there is any kind of
    ** error, return ((unsigned int)-1).
    */
    static Pgno pagerPagecount( BtShared pBt )
    {
      int nPage = -1;
      int rc;
      Debug.Assert( pBt.pPage1 != null );
      rc = sqlite3PagerPagecount( pBt.pPager, ref nPage );
      Debug.Assert( rc == SQLITE_OK || nPage == -1 );
      return (Pgno)nPage;
    }

    /*
    ** Get a page from the pager and initialize it.  This routine is just a
    ** convenience wrapper around separate calls to btreeGetPage() and
    ** btreeInitPage().
    **
    ** If an error occurs, then the value ppPage is set to is undefined. It
    ** may remain unchanged, or it may be set to an invalid value.
    */
    static int getAndInitPage(
    BtShared pBt,          /* The database file */
    Pgno pgno,             /* Number of the page to get */
    ref MemPage ppPage     /* Write the page pointer here */
    )
    {
      int rc;
#if !NDEBUG || SQLITE_COVERAGE_TEST
      Pgno iLastPg = pagerPagecount( pBt );//  TESTONLY( Pgno iLastPg = pagerPagecount(pBt); )
#else
const Pgno iLastPg = Pgno.MaxValue;
#endif
      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );

      rc = btreeGetPage( pBt, pgno, ref ppPage, 0 );
      if ( rc == SQLITE_OK )
      {
        rc = btreeInitPage( ppPage );
        if ( rc != SQLITE_OK )
        {
          releasePage( ppPage );
        }
      }

      /* If the requested page number was either 0 or greater than the page
      ** number of the last page in the database, this function should return
      ** SQLITE_CORRUPT or some other error (i.e. SQLITE_FULL). Check that this
      ** is the case.  */
      Debug.Assert( ( pgno > 0 && pgno <= iLastPg ) || rc != SQLITE_OK );
      testcase( pgno == 0 );
      testcase( pgno == iLastPg );

      return rc;
    }

    /*
    ** Release a MemPage.  This should be called once for each prior
    ** call to btreeGetPage.
    */
    static void releasePage( MemPage pPage )
    {
      if ( pPage != null )
      {
        Debug.Assert( pPage.aData != null );
        Debug.Assert( pPage.pBt != null );
        Debug.Assert( sqlite3PagerGetExtra( pPage.pDbPage ) == pPage );
        Debug.Assert( sqlite3PagerGetData( pPage.pDbPage ) == pPage.aData );
        Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
        sqlite3PagerUnref( pPage.pDbPage );
      }
    }

    /*
    ** During a rollback, when the pager reloads information into the cache
    ** so that the cache is restored to its original state at the start of
    ** the transaction, for each page restored this routine is called.
    **
    ** This routine needs to reset the extra data section at the end of the
    ** page to agree with the restored data.
    */
    static void pageReinit( DbPage pData )
    {
      MemPage pPage;
      pPage = sqlite3PagerGetExtra( pData );
      Debug.Assert( sqlite3PagerPageRefcount( pData ) > 0 );
      if ( pPage.isInit != 0 )
      {
        Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
        pPage.isInit = 0;
        if ( sqlite3PagerPageRefcount( pData ) > 1 )
        {
          /* pPage might not be a btree page;  it might be an overflow page
          ** or ptrmap page or a free page.  In those cases, the following
          ** call to btreeInitPage() will likely return SQLITE_CORRUPT.
          ** But no harm is done by this.  And it is very important that
          ** btreeInitPage() be called on every btree page so we make
          ** the call for every page that comes in for re-initing. */
          btreeInitPage( pPage );
        }
      }
    }

    /*
    ** Invoke the busy handler for a btree.
    */
    static int btreeInvokeBusyHandler( object pArg )
    {
      BtShared pBt = (BtShared)pArg;
      Debug.Assert( pBt.db != null );
      Debug.Assert( sqlite3_mutex_held( pBt.db.mutex ) );
      return sqlite3InvokeBusyHandler( pBt.db.busyHandler );
    }

    /*
    ** Open a database file.
    **
    ** zFilename is the name of the database file.  If zFilename is NULL
    ** a new database with a random name is created.  This randomly named
    ** database file will be deleted when sqlite3BtreeClose() is called.
    ** If zFilename is ":memory:" then an in-memory database is created
    ** that is automatically destroyed when it is closed.
    **
    ** If the database is already opened in the same database connection
    ** and we are in shared cache mode, then the open will fail with an
    ** SQLITE_CONSTRAINT error.  We cannot allow two or more BtShared
    ** objects in the same database connection since doing so will lead
    ** to problems with locking.
    */
    static int sqlite3BtreeOpen(
    string zFilename,       /* Name of the file containing the BTree database */
    sqlite3 db,             /* Associated database handle */
    ref Btree ppBtree,      /* Pointer to new Btree object written here */
    int flags,              /* Options */
    int vfsFlags            /* Flags passed through to sqlite3_vfs.xOpen() */
    )
    {
      sqlite3_vfs pVfs;             /* The VFS to use for this btree */
      BtShared pBt = null;          /* Shared part of btree structure */
      Btree p;                      /* Handle to return */
      sqlite3_mutex mutexOpen = null;  /* Prevents a race condition. Ticket #3537 */
      int rc = SQLITE_OK;            /* Result code from this function */
      u8 nReserve;                   /* byte of unused space on each page */
      byte[] zDbHeader = new byte[100]; /* Database header content */

      /* Set the variable isMemdb to true for an in-memory database, or
      ** false for a file-based database. This symbol is only required if
      ** either of the shared-data or autovacuum features are compiled
      ** into the library.
      */
#if !(SQLITE_OMIT_SHARED_CACHE) || !(SQLITE_OMIT_AUTOVACUUM)
#if SQLITE_OMIT_MEMORYDB
bool isMemdb = false;
#else
      bool isMemdb = zFilename == ":memory:";
#endif
#endif

      Debug.Assert( db != null );
      Debug.Assert( sqlite3_mutex_held( db.mutex ) );

      pVfs = db.pVfs;
      p = new Btree();//sqlite3MallocZero(sizeof(Btree));
      //if( !p ){
      //  return SQLITE_NOMEM;
      //}
      p.inTrans = TRANS_NONE;
      p.db = db;
#if !SQLITE_OMIT_SHARED_CACHE
p.lock.pBtree = p;
p.lock.iTable = 1;
#endif

#if !(SQLITE_OMIT_SHARED_CACHE) && !(SQLITE_OMIT_DISKIO)
/*
** If this Btree is a candidate for shared cache, try to find an
** existing BtShared object that we can share with
*/
if( isMemdb==null && zFilename && zFilename[0] ){
if( vfsFlags & SQLITE_OPEN_SHAREDCACHE ){
int nFullPathname = pVfs.mxPathname+1;
string zFullPathname = sqlite3Malloc(nFullPathname);
sqlite3_mutex *mutexShared;
p.sharable = 1;
if( !zFullPathname ){
p = null;//sqlite3_free(ref p);
return SQLITE_NOMEM;
}
sqlite3OsFullPathname(pVfs, zFilename, nFullPathname, zFullPathname);
mutexOpen = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_OPEN);
sqlite3_mutex_enter(mutexOpen);
mutexShared = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
sqlite3_mutex_enter(mutexShared);
for(pBt=GLOBAL(BtShared*,sqlite3SharedCacheList); pBt; pBt=pBt.pNext){
Debug.Assert( pBt.nRef>0 );
if( 0==strcmp(zFullPathname, sqlite3PagerFilename(pBt.pPager))
&& sqlite3PagerVfs(pBt.pPager)==pVfs ){
int iDb;
for(iDb=db.nDb-1; iDb>=0; iDb--){
Btree pExisting = db.aDb[iDb].pBt;
if( pExisting && pExisting.pBt==pBt ){
sqlite3_mutex_leave(mutexShared);
sqlite3_mutex_leave(mutexOpen);
zFullPathname = null;//sqlite3_free(ref zFullPathname);
p=null;//sqlite3_free(ref p);
return SQLITE_CONSTRAINT;
}
}
p.pBt = pBt;
pBt.nRef++;
break;
}
}
sqlite3_mutex_leave(mutexShared);
zFullPathname=null;//sqlite3_free(ref zFullPathname);
}
#if SQLITE_DEBUG
else{
/* In debug mode, we mark all persistent databases as sharable
** even when they are not.  This exercises the locking code and
** gives more opportunity for asserts(sqlite3_mutex_held())
** statements to find locking problems.
*/
p.sharable = 1;
}
#endif
}
#endif
      if ( pBt == null )
      {
        /*
        ** The following asserts make sure that structures used by the btree are
        ** the right size.  This is to guard against size changes that result
        ** when compiling on a different architecture.
        */
        Debug.Assert( sizeof( i64 ) == 8 || sizeof( i64 ) == 4 );
        Debug.Assert( sizeof( u64 ) == 8 || sizeof( u64 ) == 4 );
        Debug.Assert( sizeof( u32 ) == 4 );
        Debug.Assert( sizeof( u16 ) == 2 );
        Debug.Assert( sizeof( Pgno ) == 4 );

        pBt = new BtShared();//sqlite3MallocZero( sizeof(pBt) );
        //if( pBt==null ){
        //  rc = SQLITE_NOMEM;
        //  goto btree_open_out;
        //}
        rc = sqlite3PagerOpen( pVfs, ref pBt.pPager, zFilename,
        EXTRA_SIZE, flags, vfsFlags, pageReinit );
        if ( rc == SQLITE_OK )
        {
          rc = sqlite3PagerReadFileheader( pBt.pPager, zDbHeader.Length, zDbHeader );
        }
        if ( rc != SQLITE_OK )
        {
          goto btree_open_out;
        }
        pBt.db = db;
        sqlite3PagerSetBusyhandler( pBt.pPager, btreeInvokeBusyHandler, pBt );
        p.pBt = pBt;

        pBt.pCursor = null;
        pBt.pPage1 = null;
        pBt.readOnly = sqlite3PagerIsreadonly( pBt.pPager );
#if SQLITE_SECURE_DELETE
            pBt.secureDelete = true;
#endif
        pBt.pageSize = (u16)get2byte(zDbHeader, 16);
        if ( pBt.pageSize < 512 || pBt.pageSize > SQLITE_MAX_PAGE_SIZE
        || ( ( pBt.pageSize - 1 ) & pBt.pageSize ) != 0 )
        {
          pBt.pageSize = 0;
#if !SQLITE_OMIT_AUTOVACUUM
          /* If the magic name ":memory:" will create an in-memory database, then
** leave the autoVacuum mode at 0 (do not auto-vacuum), even if
** SQLITE_DEFAULT_AUTOVACUUM is true. On the other hand, if
** SQLITE_OMIT_MEMORYDB has been defined, then ":memory:" is just a
** regular file-name. In this case the auto-vacuum applies as per normal.
*/
          if ( zFilename != "" && !isMemdb )
          {
            pBt.autoVacuum = ( SQLITE_DEFAULT_AUTOVACUUM != 0 );
            pBt.incrVacuum = ( SQLITE_DEFAULT_AUTOVACUUM == 2 );
          }
#endif
          nReserve = 0;
        }
        else
        {
          nReserve = zDbHeader[20];
          pBt.pageSizeFixed = true;
#if !SQLITE_OMIT_AUTOVACUUM
          pBt.autoVacuum = sqlite3Get4byte( zDbHeader, 36 + 4 * 4 ) != 0;
          pBt.incrVacuum = sqlite3Get4byte( zDbHeader, 36 + 7 * 4 ) != 0;
#endif
        }
        rc = sqlite3PagerSetPagesize( pBt.pPager, ref pBt.pageSize, nReserve );
        if ( rc != 0 ) goto btree_open_out;
        pBt.usableSize = (u16)( pBt.pageSize - nReserve );
        Debug.Assert( ( pBt.pageSize & 7 ) == 0 );  /* 8-byte alignment of pageSize */

#if !(SQLITE_OMIT_SHARED_CACHE) && !(SQLITE_OMIT_DISKIO)
/* Add the new BtShared object to the linked list sharable BtShareds.
*/
if( p.sharable ){
sqlite3_mutex *mutexShared;
pBt.nRef = 1;
mutexShared = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
if( SQLITE_THREADSAFE && sqlite3GlobalConfig.bCoreMutex ){
pBt.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_FAST);
if( pBt.mutex==null ){
rc = SQLITE_NOMEM;
db.mallocFailed = 0;
goto btree_open_out;
}
}
sqlite3_mutex_enter(mutexShared);
pBt.pNext = GLOBAL(BtShared*,sqlite3SharedCacheList);
GLOBAL(BtShared*,sqlite3SharedCacheList) = pBt;
sqlite3_mutex_leave(mutexShared);
}
#endif
      }

#if !(SQLITE_OMIT_SHARED_CACHE) && !(SQLITE_OMIT_DISKIO)
/* If the new Btree uses a sharable pBtShared, then link the new
** Btree into the list of all sharable Btrees for the same connection.
** The list is kept in ascending order by pBt address.
*/
if( p.sharable ){
int i;
Btree pSib;
for(i=0; i<db.nDb; i++){
if( (pSib = db.aDb[i].pBt)!=null && pSib.sharable ){
while( pSib.pPrev ){ pSib = pSib.pPrev; }
if( p.pBt<pSib.pBt ){
p.pNext = pSib;
p.pPrev = 0;
pSib.pPrev = p;
}else{
while( pSib.pNext && pSib.pNext.pBt<p.pBt ){
pSib = pSib.pNext;
}
p.pNext = pSib.pNext;
p.pPrev = pSib;
if( p.pNext ){
p.pNext.pPrev = p;
}
pSib.pNext = p;
}
break;
}
}
}
#endif
      ppBtree = p;

    btree_open_out:
      if ( rc != SQLITE_OK )
      {
        if ( pBt != null && pBt.pPager != null )
        {
          sqlite3PagerClose( pBt.pPager );
        }
        pBt = null; //    sqlite3_free(ref pBt);
        p = null; //    sqlite3_free(ref p);
        ppBtree = null;
      }
      if ( mutexOpen != null )
      {
        Debug.Assert( sqlite3_mutex_held( mutexOpen ) );
        sqlite3_mutex_leave( mutexOpen );
      }
      return rc;
    }

    /*
    ** Decrement the BtShared.nRef counter.  When it reaches zero,
    ** remove the BtShared structure from the sharing list.  Return
    ** true if the BtShared.nRef counter reaches zero and return
    ** false if it is still positive.
    */
    static bool removeFromSharingList( BtShared pBt )
    {
#if !SQLITE_OMIT_SHARED_CACHE
sqlite3_mutex pMaster;
BtShared pList;
bool removed = false;

Debug.Assert( sqlite3_mutex_notheld(pBt.mutex) );
pMaster = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
sqlite3_mutex_enter(pMaster);
pBt.nRef--;
if( pBt.nRef<=0 ){
if( GLOBAL(BtShared*,sqlite3SharedCacheList)==pBt ){
GLOBAL(BtShared*,sqlite3SharedCacheList) = pBt.pNext;
}else{
pList = GLOBAL(BtShared*,sqlite3SharedCacheList);
while( ALWAYS(pList) && pList.pNext!=pBt ){
pList=pList.pNext;
}
if( ALWAYS(pList) ){
pList.pNext = pBt.pNext;
}
}
if( SQLITE_THREADSAFE ){
sqlite3_mutex_free(pBt.mutex);
}
removed = true;
}
sqlite3_mutex_leave(pMaster);
return removed;
#else
      return true;
#endif
    }

    /*
    ** Make sure pBt.pTmpSpace points to an allocation of
    ** MX_CELL_SIZE(pBt) bytes.
    */
    static void allocateTempSpace( BtShared pBt )
    {
      if ( null == pBt.pTmpSpace )
      {
        pBt.pTmpSpace = sqlite3Malloc(pBt.pageSize);
      }
    }

    /*
    ** Free the pBt.pTmpSpace allocation
    */
    static void freeTempSpace( BtShared pBt )
    {
      sqlite3PageFree(ref pBt.pTmpSpace);
    }

    /*
** Close an open database and invalidate all cursors.
*/
    static int sqlite3BtreeClose( ref Btree p )
    {
      BtShared pBt = p.pBt;
      BtCursor pCur;

      /* Close all cursors opened via this handle.  */
      Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
      sqlite3BtreeEnter( p );
      pCur = pBt.pCursor;
      while ( pCur != null )
      {
        BtCursor pTmp = pCur;
        pCur = pCur.pNext;
        if ( pTmp.pBtree == p )
        {
          sqlite3BtreeCloseCursor( pTmp );
        }
        sqlite3MemFreeBtCursor( ref pBt.pCursor );
      }

      /* Rollback any active transaction and free the handle structure.
      ** The call to sqlite3BtreeRollback() drops any table-locks held by
      ** this handle.
      */
      sqlite3BtreeRollback( p );
      sqlite3BtreeLeave( p );

      /* If there are still other outstanding references to the shared-btree
      ** structure, return now. The remainder of this procedure cleans
      ** up the shared-btree.
      */
      Debug.Assert( p.wantToLock == 0 && !p.locked );
      if ( !p.sharable || removeFromSharingList( pBt ) )
      {
        /* The pBt is no longer on the sharing list, so we can access
        ** it without having to hold the mutex.
        **
        ** Clean out and delete the BtShared object.
        */
        Debug.Assert( null == pBt.pCursor );
        sqlite3PagerClose( pBt.pPager );
        if ( pBt.xFreeSchema != null && pBt.pSchema != null )
        {
          pBt.xFreeSchema( pBt.pSchema );
        }
        pBt.pSchema = null;// sqlite3_free( ref pBt.pSchema );
        //freeTempSpace(pBt);
        pBt = null; //sqlite3_free(ref pBt);
      }

#if !SQLITE_OMIT_SHARED_CACHE
Debug.Assert( p.wantToLock==null );
Debug.Assert( p.locked==null );
if( p.pPrev ) p.pPrev.pNext = p.pNext;
if( p.pNext ) p.pNext.pPrev = p.pPrev;
#endif

      //sqlite3_free(ref p);
      return SQLITE_OK;
    }

    /*
    ** Change the limit on the number of pages allowed in the cache.
    **
    ** The maximum number of cache pages is set to the absolute
    ** value of mxPage.  If mxPage is negative, the pager will
    ** operate asynchronously - it will not stop to do fsync()s
    ** to insure data is written to the disk surface before
    ** continuing.  Transactions still work if synchronous is off,
    ** and the database cannot be corrupted if this program
    ** crashes.  But if the operating system crashes or there is
    ** an abrupt power failure when synchronous is off, the database
    ** could be left in an inconsistent and unrecoverable state.
    ** Synchronous is on by default so database corruption is not
    ** normally a worry.
    */
    static int sqlite3BtreeSetCacheSize( Btree p, int mxPage )
    {
      BtShared pBt = p.pBt;
      Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
      sqlite3BtreeEnter( p );
      sqlite3PagerSetCachesize( pBt.pPager, mxPage );
      sqlite3BtreeLeave( p );
      return SQLITE_OK;
    }

    /*
    ** Change the way data is synced to disk in order to increase or decrease
    ** how well the database resists damage due to OS crashes and power
    ** failures.  Level 1 is the same as asynchronous (no syncs() occur and
    ** there is a high probability of damage)  Level 2 is the default.  There
    ** is a very low but non-zero probability of damage.  Level 3 reduces the
    ** probability of damage to near zero but with a write performance reduction.
    */
#if !SQLITE_OMIT_PAGER_PRAGMAS
    static int sqlite3BtreeSetSafetyLevel( Btree p, int level, int fullSync )
    {
      BtShared pBt = p.pBt;
      Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
      sqlite3BtreeEnter( p );
      sqlite3PagerSetSafetyLevel( pBt.pPager, level, fullSync != 0 );
      sqlite3BtreeLeave( p );
      return SQLITE_OK;
    }
#endif

    /*
** Return TRUE if the given btree is set to safety level 1.  In other
** words, return TRUE if no sync() occurs on the disk files.
*/
    static int sqlite3BtreeSyncDisabled( Btree p )
    {
      BtShared pBt = p.pBt;
      int rc;
      Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
      sqlite3BtreeEnter( p );
      Debug.Assert( pBt != null && pBt.pPager != null );
      rc = sqlite3PagerNosync( pBt.pPager ) ? 1 : 0;
      sqlite3BtreeLeave( p );
      return rc;
    }

#if !(SQLITE_OMIT_PAGER_PRAGMAS) || !(SQLITE_OMIT_VACUUM)
    /*
** Change the default pages size and the number of reserved bytes per page.
** Or, if the page size has already been fixed, return SQLITE_READONLY
** without changing anything.
**
** The page size must be a power of 2 between 512 and 65536.  If the page
** size supplied does not meet this constraint then the page size is not
** changed.
**
** Page sizes are constrained to be a power of two so that the region
** of the database file used for locking (beginning at PENDING_BYTE,
** the first byte past the 1GB boundary, 0x40000000) needs to occur
** at the beginning of a page.
**
** If parameter nReserve is less than zero, then the number of reserved
** bytes per page is left unchanged.
**
** If the iFix!=null then the pageSizeFixed flag is set so that the page size
** and autovacuum mode can no longer be changed.
*/
    static int sqlite3BtreeSetPageSize( Btree p, int pageSize, int nReserve, int iFix )
    {
      int rc = SQLITE_OK;
      BtShared pBt = p.pBt;
      Debug.Assert( nReserve >= -1 && nReserve <= 255 );
      sqlite3BtreeEnter( p );
      if ( pBt.pageSizeFixed )
      {
        sqlite3BtreeLeave( p );
        return SQLITE_READONLY;
      }
      if ( nReserve < 0 )
      {
        nReserve = pBt.pageSize - pBt.usableSize;
      }
      Debug.Assert( nReserve >= 0 && nReserve <= 255 );
      if ( pageSize >= 512 && pageSize <= SQLITE_MAX_PAGE_SIZE &&
      ( ( pageSize - 1 ) & pageSize ) == 0 )
      {
        Debug.Assert( ( pageSize & 7 ) == 0 );
        Debug.Assert( null == pBt.pPage1 && null == pBt.pCursor );
        pBt.pageSize = (u16)pageSize;
        //        freeTempSpace(pBt);
      }
      rc = sqlite3PagerSetPagesize( pBt.pPager, ref pBt.pageSize, nReserve );
      pBt.usableSize = (u16)( pBt.pageSize - nReserve );
      if ( iFix != 0 ) pBt.pageSizeFixed = true;
      sqlite3BtreeLeave( p );
      return rc;
    }

    /*
    ** Return the currently defined page size
    */
    static int sqlite3BtreeGetPageSize( Btree p )
    {
      return p.pBt.pageSize;
    }

    /*
    ** Return the number of bytes of space at the end of every page that
    ** are intentually left unused.  This is the "reserved" space that is
    ** sometimes used by extensions.
    */
    static int sqlite3BtreeGetReserve( Btree p )
    {
      int n;
      sqlite3BtreeEnter( p );
      n = p.pBt.pageSize - p.pBt.usableSize;
      sqlite3BtreeLeave( p );
      return n;
    }

    /*
    ** Set the maximum page count for a database if mxPage is positive.
    ** No changes are made if mxPage is 0 or negative.
    ** Regardless of the value of mxPage, return the maximum page count.
    */
    static int sqlite3BtreeMaxPageCount( Btree p, int mxPage )
    {
      int n;
      sqlite3BtreeEnter( p );
      n = (int)sqlite3PagerMaxPageCount( p.pBt.pPager, mxPage );
      sqlite3BtreeLeave( p );
      return n;
    }

    /*
    ** Set the secureDelete flag if newFlag is 0 or 1.  If newFlag is -1,
    ** then make no changes.  Always return the value of the secureDelete
    ** setting after the change.
    */
    static int sqlite3BtreeSecureDelete(Btree p, int newFlag)
    {
      int b;
      if (p == null) return 0;
      sqlite3BtreeEnter(p);
      if (newFlag >= 0)
      {
        p.pBt.secureDelete = (newFlag != 0);
      }
      b = p.pBt.secureDelete ? 1 : 0;
      sqlite3BtreeLeave(p);
      return b;
    }
#endif //* !(SQLITE_OMIT_PAGER_PRAGMAS) || !(SQLITE_OMIT_VACUUM) */

    /*
** Change the 'auto-vacuum' property of the database. If the 'autoVacuum'
** parameter is non-zero, then auto-vacuum mode is enabled. If zero, it
** is disabled. The default value for the auto-vacuum property is
** determined by the SQLITE_DEFAULT_AUTOVACUUM macro.
*/
    static int sqlite3BtreeSetAutoVacuum( Btree p, int autoVacuum )
    {
#if SQLITE_OMIT_AUTOVACUUM
return SQLITE_READONLY;
#else
      BtShared pBt = p.pBt;
      int rc = SQLITE_OK;
      u8 av = (u8)autoVacuum;

      sqlite3BtreeEnter( p );
      if ( pBt.pageSizeFixed && ( av != 0 ) != pBt.autoVacuum )
      {
        rc = SQLITE_READONLY;
      }
      else
      {
        pBt.autoVacuum = av != 0;
        pBt.incrVacuum = av == 2;
      }
      sqlite3BtreeLeave( p );
      return rc;
#endif
    }

    /*
    ** Return the value of the 'auto-vacuum' property. If auto-vacuum is
    ** enabled 1 is returned. Otherwise 0.
    */
    static int sqlite3BtreeGetAutoVacuum( Btree p )
    {
#if SQLITE_OMIT_AUTOVACUUM
return BTREE_AUTOVACUUM_NONE;
#else
      int rc;
      sqlite3BtreeEnter( p );
      rc = (
      ( !p.pBt.autoVacuum ) ? BTREE_AUTOVACUUM_NONE :
      ( !p.pBt.incrVacuum ) ? BTREE_AUTOVACUUM_FULL :
      BTREE_AUTOVACUUM_INCR
      );
      sqlite3BtreeLeave( p );
      return rc;
#endif
    }


    /*
    ** Get a reference to pPage1 of the database file.  This will
    ** also acquire a readlock on that file.
    **
    ** SQLITE_OK is returned on success.  If the file is not a
    ** well-formed database file, then SQLITE_CORRUPT is returned.
    ** SQLITE_BUSY is returned if the database is locked.  SQLITE_NOMEM
    ** is returned if we run out of memory.
    */
    static int lockBtree( BtShared pBt )
    {
      int rc;
      MemPage pPage1 = new MemPage();
      int nPage = 0;

      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      Debug.Assert( pBt.pPage1 == null );
      rc = sqlite3PagerSharedLock( pBt.pPager );
      if ( rc != SQLITE_OK ) return rc;
      rc = btreeGetPage( pBt, 1, ref pPage1, 0 );
      if ( rc != SQLITE_OK ) return rc;

      /* Do some checking to help insure the file we opened really is
      ** a valid database file.
      */
      rc = sqlite3PagerPagecount( pBt.pPager, ref nPage );
      if ( rc != SQLITE_OK )
      {
        goto page1_init_failed;
      }
      else if ( nPage > 0 )
      {
        int pageSize;
        int usableSize;
        u8[] page1 = pPage1.aData;
        rc = SQLITE_NOTADB;
        if ( memcmp( page1, zMagicHeader, 16 ) != 0 )
        {
          goto page1_init_failed;
        }
        if ( page1[18] > 1 )
        {
          pBt.readOnly = true;
        }
        if ( page1[19] > 1 )
        {
          goto page1_init_failed;
        }

        /* The maximum embedded fraction must be exactly 25%.  And the minimum
        ** embedded fraction must be 12.5% for both leaf-data and non-leaf-data.
        ** The original design allowed these amounts to vary, but as of
        ** version 3.6.0, we require them to be fixed.
        */
        if ( memcmp( page1, 21, "\x0040\x0020\x0020", 3 ) != 0 )//   "\100\040\040"
        {
          goto page1_init_failed;
        }
        pageSize = get2byte( page1, 16 );
        if ( ( ( pageSize - 1 ) & pageSize ) != 0 || pageSize < 512 ||
        ( SQLITE_MAX_PAGE_SIZE < 32768 && pageSize > SQLITE_MAX_PAGE_SIZE )
        )
        {
          goto page1_init_failed;
        }
        Debug.Assert( ( pageSize & 7 ) == 0 );
        usableSize = pageSize - page1[20];
        if ( pageSize != pBt.pageSize )
        {
          /* After reading the first page of the database assuming a page size
          ** of BtShared.pageSize, we have discovered that the page-size is
          ** actually pageSize. Unlock the database, leave pBt.pPage1 at
          ** zero and return SQLITE_OK. The caller will call this function
          ** again with the correct page-size.
          */
          releasePage( pPage1 );
          pBt.usableSize = (u16)usableSize;
          pBt.pageSize = (u16)pageSize;
          //          freeTempSpace(pBt);
          rc = sqlite3PagerSetPagesize( pBt.pPager, ref pBt.pageSize,
          pageSize - usableSize );
          return rc;
        }
        if ( usableSize < 480 )
        {
          goto page1_init_failed;
        }
        pBt.pageSize = (u16)pageSize;
        pBt.usableSize = (u16)usableSize;
#if !SQLITE_OMIT_AUTOVACUUM
        pBt.autoVacuum = ( sqlite3Get4byte( page1, 36 + 4 * 4 ) != 0 );
        pBt.incrVacuum = ( sqlite3Get4byte( page1, 36 + 7 * 4 ) != 0 );
#endif
      }

      /* maxLocal is the maximum amount of payload to store locally for
      ** a cell.  Make sure it is small enough so that at least minFanout
      ** cells can will fit on one page.  We assume a 10-byte page header.
      ** Besides the payload, the cell must store:
      **     2-byte pointer to the cell
      **     4-byte child pointer
      **     9-byte nKey value
      **     4-byte nData value
      **     4-byte overflow page pointer
      ** So a cell consists of a 2-byte poiner, a header which is as much as
      ** 17 bytes long, 0 to N bytes of payload, and an optional 4 byte overflow
      ** page pointer.
      */
      pBt.maxLocal = (u16)( ( pBt.usableSize - 12 ) * 64 / 255 - 23 );
      pBt.minLocal = (u16)( ( pBt.usableSize - 12 ) * 32 / 255 - 23 );
      pBt.maxLeaf = (u16)( pBt.usableSize - 35 );
      pBt.minLeaf = (u16)( ( pBt.usableSize - 12 ) * 32 / 255 - 23 );
      Debug.Assert( pBt.maxLeaf + 23 <= MX_CELL_SIZE( pBt ) );
      pBt.pPage1 = pPage1;
      return SQLITE_OK;

    page1_init_failed:
      releasePage( pPage1 );
      pBt.pPage1 = null;
      return rc;
    }

    /*
    ** If there are no outstanding cursors and we are not in the middle
    ** of a transaction but there is a read lock on the database, then
    ** this routine unrefs the first page of the database file which
    ** has the effect of releasing the read lock.
    **
    ** If there is a transaction in progress, this routine is a no-op.
    */
    static void unlockBtreeIfUnused( BtShared pBt )
    {
      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      Debug.Assert( pBt.pCursor == null || pBt.inTransaction > TRANS_NONE );
      if ( pBt.inTransaction == TRANS_NONE && pBt.pPage1 != null )
      {
        Debug.Assert( pBt.pPage1.aData != null );
        Debug.Assert( sqlite3PagerRefcount( pBt.pPager ) == 1 );
        Debug.Assert( pBt.pPage1.aData != null );
        releasePage( pBt.pPage1 );
        pBt.pPage1 = null;
      }
    }

    /*
    ** If pBt points to an empty file then convert that empty file
    ** into a new empty database by initializing the first page of
    ** the database.
    */
    static int newDatabase( BtShared pBt )
    {
      MemPage pP1;
      byte[] data;
      int rc;
      int nPage = 0;

      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      rc = sqlite3PagerPagecount( pBt.pPager, ref nPage );
      if ( rc != SQLITE_OK || nPage > 0 )
      {
        return rc;
      }
      pP1 = pBt.pPage1;
      Debug.Assert( pP1 != null );
      data = pP1.aData;
      rc = sqlite3PagerWrite( pP1.pDbPage );
      if ( rc != 0 ) return rc;
      Buffer.BlockCopy( Encoding.UTF8.GetBytes( zMagicHeader ), 0, data, 0, 16 );// memcpy(data, zMagicHeader, sizeof(zMagicHeader));
      Debug.Assert( zMagicHeader.Length == 16 );
      put2byte( data, 16, pBt.pageSize );
      data[18] = 1;
      data[19] = 1;
      Debug.Assert( pBt.usableSize <= pBt.pageSize && pBt.usableSize + 255 >= pBt.pageSize );
      data[20] = (u8)( pBt.pageSize - pBt.usableSize );
      data[21] = 64;
      data[22] = 32;
      data[23] = 32;
      //memset(&data[24], 0, 100-24);
      zeroPage( pP1, PTF_INTKEY | PTF_LEAF | PTF_LEAFDATA );
      pBt.pageSizeFixed = true;
#if !SQLITE_OMIT_AUTOVACUUM
      Debug.Assert( pBt.autoVacuum == true || pBt.autoVacuum == false );
      Debug.Assert( pBt.incrVacuum == true || pBt.incrVacuum == false );
      sqlite3Put4byte( data, 36 + 4 * 4, pBt.autoVacuum ? 1 : 0 );
      sqlite3Put4byte( data, 36 + 7 * 4, pBt.incrVacuum ? 1 : 0 );
#endif
      return SQLITE_OK;
    }

    /*
    ** Attempt to start a new transaction. A write-transaction
    ** is started if the second argument is nonzero, otherwise a read-
    ** transaction.  If the second argument is 2 or more and exclusive
    ** transaction is started, meaning that no other process is allowed
    ** to access the database.  A preexisting transaction may not be
    ** upgraded to exclusive by calling this routine a second time - the
    ** exclusivity flag only works for a new transaction.
    **
    ** A write-transaction must be started before attempting any
    ** changes to the database.  None of the following routines
    ** will work unless a transaction is started first:
    **
    **      sqlite3BtreeCreateTable()
    **      sqlite3BtreeCreateIndex()
    **      sqlite3BtreeClearTable()
    **      sqlite3BtreeDropTable()
    **      sqlite3BtreeInsert()
    **      sqlite3BtreeDelete()
    **      sqlite3BtreeUpdateMeta()
    **
    ** If an initial attempt to acquire the lock fails because of lock contention
    ** and the database was previously unlocked, then invoke the busy handler
    ** if there is one.  But if there was previously a read-lock, do not
    ** invoke the busy handler - just return SQLITE_BUSY.  SQLITE_BUSY is
    ** returned when there is already a read-lock in order to avoid a deadlock.
    **
    ** Suppose there are two processes A and B.  A has a read lock and B has
    ** a reserved lock.  B tries to promote to exclusive but is blocked because
    ** of A's read lock.  A tries to promote to reserved but is blocked by B.
    ** One or the other of the two processes must give way or there can be
    ** no progress.  By returning SQLITE_BUSY and not invoking the busy callback
    ** when A already has a read lock, we encourage A to give up and let B
    ** proceed.
    */
    static int sqlite3BtreeBeginTrans( Btree p, int wrflag )
    {
      BtShared pBt = p.pBt;
      int rc = SQLITE_OK;

      sqlite3BtreeEnter( p );
      btreeIntegrity( p );

      /* If the btree is already in a write-transaction, or it
      ** is already in a read-transaction and a read-transaction
      ** is requested, this is a no-op.
      */
      if ( p.inTrans == TRANS_WRITE || ( p.inTrans == TRANS_READ && 0 == wrflag ) )
      {
        goto trans_begun;
      }

      /* Write transactions are not possible on a read-only database */
      if ( pBt.readOnly && wrflag != 0 )
      {
        rc = SQLITE_READONLY;
        goto trans_begun;
      }

#if !SQLITE_OMIT_SHARED_CACHE
/* If another database handle has already opened a write transaction
** on this shared-btree structure and a second write transaction is
** requested, return SQLITE_LOCKED.
*/
if( (wrflag && pBt.inTransaction==TRANS_WRITE) || pBt.isPending ){
sqlite3 pBlock = pBt.pWriter.db;
}else if( wrflag>1 ){
BtLock pIter;
for(pIter=pBt.pLock; pIter; pIter=pIter.pNext){
if( pIter.pBtree!=p ){
pBlock = pIter.pBtree.db;
break;
}
}
}
if( pBlock ){
sqlite3ConnectionBlocked(p.db, pBlock);
rc = SQLITE_LOCKED_SHAREDCACHE;
goto trans_begun;
}
#endif

      /* Any read-only or read-write transaction implies a read-lock on
** page 1. So if some other shared-cache client already has a write-lock
** on page 1, the transaction cannot be opened. */
      rc = querySharedCacheTableLock( p, MASTER_ROOT, READ_LOCK );
      if ( SQLITE_OK != rc ) goto trans_begun;

      do
      {
        /* Call lockBtree() until either pBt.pPage1 is populated or
        ** lockBtree() returns something other than SQLITE_OK. lockBtree()
        ** may return SQLITE_OK but leave pBt.pPage1 set to 0 if after
        ** reading page 1 it discovers that the page-size of the database
        ** file is not pBt.pageSize. In this case lockBtree() will update
        ** pBt.pageSize to the page-size of the file on disk.
        */
        while ( pBt.pPage1 == null && SQLITE_OK == ( rc = lockBtree( pBt ) ) ) ;

        if ( rc == SQLITE_OK && wrflag != 0 )
        {
          if ( pBt.readOnly )
          {
            rc = SQLITE_READONLY;
          }
          else
          {
            rc = sqlite3PagerBegin( pBt.pPager, wrflag > 1, sqlite3TempInMemory( p.db ) ? 1 : 0 );
            if ( rc == SQLITE_OK )
            {
              rc = newDatabase( pBt );
            }
          }
        }

        if ( rc != SQLITE_OK )
        {
          unlockBtreeIfUnused( pBt );
        }
      } while ( rc == SQLITE_BUSY && pBt.inTransaction == TRANS_NONE &&
      btreeInvokeBusyHandler( pBt ) != 0 );

      if ( rc == SQLITE_OK )
      {
        if ( p.inTrans == TRANS_NONE )
        {
          pBt.nTransaction++;
#if !SQLITE_OMIT_SHARED_CACHE
if( p.sharable ){
Debug.Assert( p.lock.pBtree==p && p.lock.iTable==1 );
p.lock.eLock = READ_LOCK;
p.lock.pNext = pBt.pLock;
pBt.pLock = &p.lock;
}
#endif
        }
        p.inTrans = ( wrflag != 0 ? TRANS_WRITE : TRANS_READ );
        if ( p.inTrans > pBt.inTransaction )
        {
          pBt.inTransaction = p.inTrans;
        }
#if !SQLITE_OMIT_SHARED_CACHE
if( wrflag ){
Debug.Assert( !pBt.pWriter );
pBt.pWriter = p;
pBt.isExclusive = (u8)(wrflag>1);
}
#endif
      }


    trans_begun:
      if ( rc == SQLITE_OK && wrflag != 0 )
      {
        /* This call makes sure that the pager has the correct number of
        ** open savepoints. If the second parameter is greater than 0 and
        ** the sub-journal is not already open, then it will be opened here.
        */
        rc = sqlite3PagerOpenSavepoint( pBt.pPager, p.db.nSavepoint );
      }

      btreeIntegrity( p );
      sqlite3BtreeLeave( p );
      return rc;
    }

#if !SQLITE_OMIT_AUTOVACUUM

    /*
** Set the pointer-map entries for all children of page pPage. Also, if
** pPage contains cells that point to overflow pages, set the pointer
** map entries for the overflow pages as well.
*/
    static int setChildPtrmaps( MemPage pPage )
    {
      int i;                             /* Counter variable */
      int nCell;                         /* Number of cells in page pPage */
      int rc;                            /* Return code */
      BtShared pBt = pPage.pBt;
      u8 isInitOrig = pPage.isInit;
      Pgno pgno = pPage.pgno;

      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      rc = btreeInitPage( pPage );
      if ( rc != SQLITE_OK )
      {
        goto set_child_ptrmaps_out;
      }
      nCell = pPage.nCell;

      for ( i = 0; i < nCell; i++ )
      {
        int pCell = findCell( pPage, i );

        ptrmapPutOvflPtr( pPage, pCell, ref rc );

        if ( 0 == pPage.leaf )
        {
          Pgno childPgno = sqlite3Get4byte( pPage.aData, pCell );
          ptrmapPut( pBt, childPgno, PTRMAP_BTREE, pgno, ref rc );
        }
      }

      if ( 0 == pPage.leaf )
      {
        Pgno childPgno = sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 );
        ptrmapPut( pBt, childPgno, PTRMAP_BTREE, pgno, ref rc );
      }

    set_child_ptrmaps_out:
      pPage.isInit = isInitOrig;
      return rc;
    }

    /*
    ** Somewhere on pPage is a pointer to page iFrom.  Modify this pointer so
    ** that it points to iTo. Parameter eType describes the type of pointer to
    ** be modified, as  follows:
    **
    ** PTRMAP_BTREE:     pPage is a btree-page. The pointer points at a child
    **                   page of pPage.
    **
    ** PTRMAP_OVERFLOW1: pPage is a btree-page. The pointer points at an overflow
    **                   page pointed to by one of the cells on pPage.
    **
    ** PTRMAP_OVERFLOW2: pPage is an overflow-page. The pointer points at the next
    **                   overflow page in the list.
    */
    static int modifyPagePointer( MemPage pPage, Pgno iFrom, Pgno iTo, u8 eType )
    {
      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
      if ( eType == PTRMAP_OVERFLOW2 )
      {
        /* The pointer is always the first 4 bytes of the page in this case.  */
        if ( sqlite3Get4byte( pPage.aData ) != iFrom )
        {
          return SQLITE_CORRUPT_BKPT();
        }
        sqlite3Put4byte( pPage.aData, iTo );
      }
      else
      {
        u8 isInitOrig = pPage.isInit;
        int i;
        int nCell;

        btreeInitPage( pPage );
        nCell = pPage.nCell;

        for ( i = 0; i < nCell; i++ )
        {
          int pCell = findCell( pPage, i );
          if ( eType == PTRMAP_OVERFLOW1 )
          {
            CellInfo info = new CellInfo();
            btreeParseCellPtr( pPage, pCell, ref info );
            if ( info.iOverflow != 0 )
            {
              if ( iFrom == sqlite3Get4byte( pPage.aData, pCell, info.iOverflow ) )
              {
                sqlite3Put4byte( pPage.aData, pCell + info.iOverflow, (int)iTo );
                break;
              }
            }
          }
          else
          {
            if ( sqlite3Get4byte( pPage.aData, pCell ) == iFrom )
            {
              sqlite3Put4byte( pPage.aData, pCell, (int)iTo );
              break;
            }
          }
        }

        if ( i == nCell )
        {
          if ( eType != PTRMAP_BTREE ||
          sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 ) != iFrom )
          {
            return SQLITE_CORRUPT_BKPT();
          }
          sqlite3Put4byte( pPage.aData, pPage.hdrOffset + 8, iTo );
        }

        pPage.isInit = isInitOrig;
      }
      return SQLITE_OK;
    }


    /*
    ** Move the open database page pDbPage to location iFreePage in the
    ** database. The pDbPage reference remains valid.
    **
    ** The isCommit flag indicates that there is no need to remember that
    ** the journal needs to be sync()ed before database page pDbPage.pgno
    ** can be written to. The caller has already promised not to write to that
    ** page.
    */
    static int relocatePage(
    BtShared pBt,           /* Btree */
    MemPage pDbPage,        /* Open page to move */
    u8 eType,                /* Pointer map 'type' entry for pDbPage */
    Pgno iPtrPage,           /* Pointer map 'page-no' entry for pDbPage */
    Pgno iFreePage,          /* The location to move pDbPage to */
    int isCommit             /* isCommit flag passed to sqlite3PagerMovepage */
    )
    {
      MemPage pPtrPage = new MemPage();   /* The page that contains a pointer to pDbPage */
      Pgno iDbPage = pDbPage.pgno;
      Pager pPager = pBt.pPager;
      int rc;

      Debug.Assert( eType == PTRMAP_OVERFLOW2 || eType == PTRMAP_OVERFLOW1 ||
      eType == PTRMAP_BTREE || eType == PTRMAP_ROOTPAGE );
      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      Debug.Assert( pDbPage.pBt == pBt );

      /* Move page iDbPage from its current location to page number iFreePage */
      TRACE( "AUTOVACUUM: Moving %d to free page %d (ptr page %d type %d)\n",
      iDbPage, iFreePage, iPtrPage, eType );
      rc = sqlite3PagerMovepage( pPager, pDbPage.pDbPage, iFreePage, isCommit );
      if ( rc != SQLITE_OK )
      {
        return rc;
      }
      pDbPage.pgno = iFreePage;

      /* If pDbPage was a btree-page, then it may have child pages and/or cells
      ** that point to overflow pages. The pointer map entries for all these
      ** pages need to be changed.
      **
      ** If pDbPage is an overflow page, then the first 4 bytes may store a
      ** pointer to a subsequent overflow page. If this is the case, then
      ** the pointer map needs to be updated for the subsequent overflow page.
      */
      if ( eType == PTRMAP_BTREE || eType == PTRMAP_ROOTPAGE )
      {
        rc = setChildPtrmaps( pDbPage );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
      }
      else
      {
        Pgno nextOvfl = sqlite3Get4byte( pDbPage.aData );
        if ( nextOvfl != 0 )
        {
          ptrmapPut( pBt, nextOvfl, PTRMAP_OVERFLOW2, iFreePage, ref rc );
          if ( rc != SQLITE_OK )
          {
            return rc;
          }
        }
      }

      /* Fix the database pointer on page iPtrPage that pointed at iDbPage so
      ** that it points at iFreePage. Also fix the pointer map entry for
      ** iPtrPage.
      */
      if ( eType != PTRMAP_ROOTPAGE )
      {
        rc = btreeGetPage( pBt, iPtrPage, ref pPtrPage, 0 );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
        rc = sqlite3PagerWrite( pPtrPage.pDbPage );
        if ( rc != SQLITE_OK )
        {
          releasePage( pPtrPage );
          return rc;
        }
        rc = modifyPagePointer( pPtrPage, iDbPage, iFreePage, eType );
        releasePage( pPtrPage );
        if ( rc == SQLITE_OK )
        {
          ptrmapPut( pBt, iFreePage, eType, iPtrPage, ref rc );
        }
      }
      return rc;
    }

    /* Forward declaration required by incrVacuumStep(). */
    //static int allocateBtreePage(BtShared *, MemPage **, Pgno *, Pgno, u8);

    /*
    ** Perform a single step of an incremental-vacuum. If successful,
    ** return SQLITE_OK. If there is no work to do (and therefore no
    ** point in calling this function again), return SQLITE_DONE.
    **
    ** More specificly, this function attempts to re-organize the
    ** database so that the last page of the file currently in use
    ** is no longer in use.
    **
    ** If the nFin parameter is non-zero, this function assumes
    ** that the caller will keep calling incrVacuumStep() until
    ** it returns SQLITE_DONE or an error, and that nFin is the
    ** number of pages the database file will contain after this
    ** process is complete.  If nFin is zero, it is assumed that
    ** incrVacuumStep() will be called a finite amount of times
    ** which may or may not empty the freelist.  A full autovacuum
    ** has nFin>0.  A "PRAGMA incremental_vacuum" has nFin==null.
    */
    static int incrVacuumStep( BtShared pBt, Pgno nFin, Pgno iLastPg )
    {
      Pgno nFreeList;           /* Number of pages still on the free-list */

      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      Debug.Assert( iLastPg > nFin );

      if ( !PTRMAP_ISPAGE( pBt, iLastPg ) && iLastPg != PENDING_BYTE_PAGE( pBt ) )
      {
        int rc;
        u8 eType = 0;
        Pgno iPtrPage = 0;

        nFreeList = sqlite3Get4byte( pBt.pPage1.aData, 36 );
        if ( nFreeList == 0 )
        {
          return SQLITE_DONE;
        }

        rc = ptrmapGet( pBt, iLastPg, ref eType, ref iPtrPage );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
        if ( eType == PTRMAP_ROOTPAGE )
        {
          return SQLITE_CORRUPT_BKPT();
        }

        if ( eType == PTRMAP_FREEPAGE )
        {
          if ( nFin == 0 )
          {
            /* Remove the page from the files free-list. This is not required
            ** if nFin is non-zero. In that case, the free-list will be
            ** truncated to zero after this function returns, so it doesn't
            ** matter if it still contains some garbage entries.
            */
            Pgno iFreePg = 0;
            MemPage pFreePg = new MemPage();
            rc = allocateBtreePage( pBt, ref pFreePg, ref iFreePg, iLastPg, 1 );
            if ( rc != SQLITE_OK )
            {
              return rc;
            }
            Debug.Assert( iFreePg == iLastPg );
            releasePage( pFreePg );
          }
        }
        else
        {
          Pgno iFreePg = 0;             /* Index of free page to move pLastPg to */
          MemPage pLastPg = new MemPage();

          rc = btreeGetPage( pBt, iLastPg, ref pLastPg, 0 );
          if ( rc != SQLITE_OK )
          {
            return rc;
          }

          /* If nFin is zero, this loop runs exactly once and page pLastPg
          ** is swapped with the first free page pulled off the free list.
          **
          ** On the other hand, if nFin is greater than zero, then keep
          ** looping until a free-page located within the first nFin pages
          ** of the file is found.
          */
          do
          {
            MemPage pFreePg = new MemPage();
            rc = allocateBtreePage( pBt, ref pFreePg, ref iFreePg, 0, 0 );
            if ( rc != SQLITE_OK )
            {
              releasePage( pLastPg );
              return rc;
            }
            releasePage( pFreePg );
          } while ( nFin != 0 && iFreePg > nFin );
          Debug.Assert( iFreePg < iLastPg );

          rc = sqlite3PagerWrite( pLastPg.pDbPage );
          if ( rc == SQLITE_OK )
          {
            rc = relocatePage( pBt, pLastPg, eType, iPtrPage, iFreePg, ( nFin != 0 ) ? 1 : 0 );
          }
          releasePage( pLastPg );
          if ( rc != SQLITE_OK )
          {
            return rc;
          }
        }
      }

      if ( nFin == 0 )
      {
        iLastPg--;
        while ( iLastPg == PENDING_BYTE_PAGE( pBt ) || PTRMAP_ISPAGE( pBt, iLastPg ) )
        {
          if ( PTRMAP_ISPAGE( pBt, iLastPg ) )
          {
            MemPage pPg = new MemPage();
            int rc = btreeGetPage( pBt, iLastPg, ref pPg, 0 );
            if ( rc != SQLITE_OK )
            {
              return rc;
            }
            rc = sqlite3PagerWrite( pPg.pDbPage );
            releasePage( pPg );
            if ( rc != SQLITE_OK )
            {
              return rc;
            }
          }
          iLastPg--;
        }
        sqlite3PagerTruncateImage( pBt.pPager, iLastPg );
      }
      return SQLITE_OK;
    }

    /*
    ** A write-transaction must be opened before calling this function.
    ** It performs a single unit of work towards an incremental vacuum.
    **
    ** If the incremental vacuum is finished after this function has run,
    ** SQLITE_DONE is returned. If it is not finished, but no error occurred,
    ** SQLITE_OK is returned. Otherwise an SQLite error code.
    */
    static int sqlite3BtreeIncrVacuum( Btree p )
    {
      int rc;
      BtShared pBt = p.pBt;

      sqlite3BtreeEnter( p );
      Debug.Assert( pBt.inTransaction == TRANS_WRITE && p.inTrans == TRANS_WRITE );
      if ( !pBt.autoVacuum )
      {
        rc = SQLITE_DONE;
      }
      else
      {
        invalidateAllOverflowCache( pBt );
        rc = incrVacuumStep( pBt, 0, pagerPagecount( pBt ) );
      }
      sqlite3BtreeLeave( p );
      return rc;
    }

    /*
    ** This routine is called prior to sqlite3PagerCommit when a transaction
    ** is commited for an auto-vacuum database.
    **
    ** If SQLITE_OK is returned, then pnTrunc is set to the number of pages
    ** the database file should be truncated to during the commit process.
    ** i.e. the database has been reorganized so that only the first pnTrunc
    ** pages are in use.
    */
    static int autoVacuumCommit( BtShared pBt )
    {
      int rc = SQLITE_OK;
      Pager pPager = pBt.pPager;
      // VVA_ONLY( int nRef = sqlite3PagerRefcount(pPager) );
#if !NDEBUG || DEBUG
      int nRef = sqlite3PagerRefcount( pPager );
#else
int nRef=0;
#endif


      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      invalidateAllOverflowCache( pBt );
      Debug.Assert( pBt.autoVacuum );
      if ( !pBt.incrVacuum )
      {
        Pgno nFin;         /* Number of pages in database after autovacuuming */
        Pgno nFree;        /* Number of pages on the freelist initially */
        Pgno nPtrmap;      /* Number of PtrMap pages to be freed */
        Pgno iFree;        /* The next page to be freed */
        int nEntry;        /* Number of entries on one ptrmap page */
        Pgno nOrig;        /* Database size before freeing */

        nOrig = pagerPagecount( pBt );
        if ( PTRMAP_ISPAGE( pBt, nOrig ) || nOrig == PENDING_BYTE_PAGE( pBt ) )
        {
          /* It is not possible to create a database for which the final page
          ** is either a pointer-map page or the pending-byte page. If one
          ** is encountered, this indicates corruption.
          */
          return SQLITE_CORRUPT_BKPT();
        }

        nFree = sqlite3Get4byte( pBt.pPage1.aData, 36 );
        nEntry = pBt.usableSize / 5;
        nPtrmap = (Pgno)( ( nFree - nOrig + PTRMAP_PAGENO( pBt, nOrig ) + (Pgno)nEntry ) / nEntry );
        nFin = nOrig - nFree - nPtrmap;
        if ( nOrig > PENDING_BYTE_PAGE( pBt ) && nFin < PENDING_BYTE_PAGE( pBt ) )
        {
          nFin--;
        }
        while ( PTRMAP_ISPAGE( pBt, nFin ) || nFin == PENDING_BYTE_PAGE( pBt ) )
        {
          nFin--;
        }
        if ( nFin > nOrig )
          return SQLITE_CORRUPT_BKPT();

        for ( iFree = nOrig; iFree > nFin && rc == SQLITE_OK; iFree-- )
        {
          rc = incrVacuumStep( pBt, nFin, iFree );
        }
        if ( ( rc == SQLITE_DONE || rc == SQLITE_OK ) && nFree > 0 )
        {
          rc = SQLITE_OK;
          rc = sqlite3PagerWrite( pBt.pPage1.pDbPage );
          sqlite3Put4byte( pBt.pPage1.aData, 32, 0 );
          sqlite3Put4byte( pBt.pPage1.aData, 36, 0 );
          sqlite3PagerTruncateImage( pBt.pPager, nFin );
        }
        if ( rc != SQLITE_OK )
        {
          sqlite3PagerRollback( pPager );
        }
      }

      Debug.Assert( nRef == sqlite3PagerRefcount( pPager ) );
      return rc;
    }

#else //* ifndef SQLITE_OMIT_AUTOVACUUM */
//# define setChildPtrmaps(x) SQLITE_OK
#endif

    /*
** This routine does the first phase of a two-phase commit.  This routine
** causes a rollback journal to be created (if it does not already exist)
** and populated with enough information so that if a power loss occurs
** the database can be restored to its original state by playing back
** the journal.  Then the contents of the journal are flushed out to
** the disk.  After the journal is safely on oxide, the changes to the
** database are written into the database file and flushed to oxide.
** At the end of this call, the rollback journal still exists on the
** disk and we are still holding all locks, so the transaction has not
** committed.  See sqlite3BtreeCommitPhaseTwo() for the second phase of the
** commit process.
**
** This call is a no-op if no write-transaction is currently active on pBt.
**
** Otherwise, sync the database file for the btree pBt. zMaster points to
** the name of a master journal file that should be written into the
** individual journal file, or is NULL, indicating no master journal file
** (single database transaction).
**
** When this is called, the master journal should already have been
** created, populated with this journal pointer and synced to disk.
**
** Once this is routine has returned, the only thing required to commit
** the write-transaction for this database file is to delete the journal.
*/
    static int sqlite3BtreeCommitPhaseOne( Btree p, string zMaster )
    {
      int rc = SQLITE_OK;
      if ( p.inTrans == TRANS_WRITE )
      {
        BtShared pBt = p.pBt;
        sqlite3BtreeEnter( p );
#if !SQLITE_OMIT_AUTOVACUUM
        if ( pBt.autoVacuum )
        {
          rc = autoVacuumCommit( pBt );
          if ( rc != SQLITE_OK )
          {
            sqlite3BtreeLeave( p );
            return rc;
          }
        }
#endif
        rc = sqlite3PagerCommitPhaseOne( pBt.pPager, zMaster, false );
        sqlite3BtreeLeave( p );
      }
      return rc;
    }

    /*
    ** This function is called from both BtreeCommitPhaseTwo() and BtreeRollback()
    ** at the conclusion of a transaction.
    */
    static void btreeEndTransaction( Btree p )
    {
      BtShared pBt = p.pBt;
      Debug.Assert( sqlite3BtreeHoldsMutex( p ) );

      btreeClearHasContent( pBt );
      if ( p.inTrans > TRANS_NONE && p.db.activeVdbeCnt > 1 )
      {
        /* If there are other active statements that belong to this database
        ** handle, downgrade to a read-only transaction. The other statements
        ** may still be reading from the database.  */

        downgradeAllSharedCacheTableLocks( p );
        p.inTrans = TRANS_READ;
      }
      else
      {
        /* If the handle had any kind of transaction open, decrement the
        ** transaction count of the shared btree. If the transaction count
        ** reaches 0, set the shared state to TRANS_NONE. The unlockBtreeIfUnused()
        ** call below will unlock the pager.  */
        if ( p.inTrans != TRANS_NONE )
        {
          clearAllSharedCacheTableLocks( p );
          pBt.nTransaction--;
          if ( 0 == pBt.nTransaction )
          {
            pBt.inTransaction = TRANS_NONE;
          }
        }

        /* Set the current transaction state to TRANS_NONE and unlock the
        ** pager if this call closed the only read or write transaction.  */
        p.inTrans = TRANS_NONE;
        unlockBtreeIfUnused( pBt );
      }

      btreeIntegrity( p );
    }

    /*
    ** Commit the transaction currently in progress.
    **
    ** This routine implements the second phase of a 2-phase commit.  The
    ** sqlite3BtreeCommitPhaseOne() routine does the first phase and should
    ** be invoked prior to calling this routine.  The sqlite3BtreeCommitPhaseOne()
    ** routine did all the work of writing information out to disk and flushing the
    ** contents so that they are written onto the disk platter.  All this
    ** routine has to do is delete or truncate or zero the header in the
    ** the rollback journal (which causes the transaction to commit) and
    ** drop locks.
    **
    ** This will release the write lock on the database file.  If there
    ** are no active cursors, it also releases the read lock.
    */
    static int sqlite3BtreeCommitPhaseTwo( Btree p )
    {
      BtShared pBt = p.pBt;

      sqlite3BtreeEnter( p );
      btreeIntegrity( p );

      /* If the handle has a write-transaction open, commit the shared-btrees
      ** transaction and set the shared state to TRANS_READ.
      */
      if ( p.inTrans == TRANS_WRITE )
      {
        int rc;
        Debug.Assert( pBt.inTransaction == TRANS_WRITE );
        Debug.Assert( pBt.nTransaction > 0 );
        rc = sqlite3PagerCommitPhaseTwo( pBt.pPager );
        if ( rc != SQLITE_OK )
        {
          sqlite3BtreeLeave( p );
          return rc;
        }
        pBt.inTransaction = TRANS_READ;
      }

      btreeEndTransaction( p );
      sqlite3BtreeLeave( p );
      return SQLITE_OK;
    }

    /*
    ** Do both phases of a commit.
    */
    static int sqlite3BtreeCommit( Btree p )
    {
      int rc;
      sqlite3BtreeEnter( p );
      rc = sqlite3BtreeCommitPhaseOne( p, null );
      if ( rc == SQLITE_OK )
      {
        rc = sqlite3BtreeCommitPhaseTwo( p );
      }
      sqlite3BtreeLeave( p );
      return rc;
    }

#if !NDEBUG || DEBUG
    /*
** Return the number of write-cursors open on this handle. This is for use
** in Debug.Assert() expressions, so it is only compiled if NDEBUG is not
** defined.
**
** For the purposes of this routine, a write-cursor is any cursor that
** is capable of writing to the databse.  That means the cursor was
** originally opened for writing and the cursor has not be disabled
** by having its state changed to CURSOR_FAULT.
*/
    static int countWriteCursors( BtShared pBt )
    {
      BtCursor pCur;
      int r = 0;
      for ( pCur = pBt.pCursor; pCur != null; pCur = pCur.pNext )
      {
        if ( pCur.wrFlag != 0 && pCur.eState != CURSOR_FAULT ) r++;
      }
      return r;
    }
#else
static int countWriteCursors(BtShared pBt) { return -1; }
#endif

    /*
** This routine sets the state to CURSOR_FAULT and the error
** code to errCode for every cursor on BtShared that pBtree
** references.
**
** Every cursor is tripped, including cursors that belong
** to other database connections that happen to be sharing
** the cache with pBtree.
**
** This routine gets called when a rollback occurs.
** All cursors using the same cache must be tripped
** to prevent them from trying to use the btree after
** the rollback.  The rollback may have deleted tables
** or moved root pages, so it is not sufficient to
** save the state of the cursor.  The cursor must be
** invalidated.
*/
    static void sqlite3BtreeTripAllCursors( Btree pBtree, int errCode )
    {
      BtCursor p;
      sqlite3BtreeEnter( pBtree );
      for ( p = pBtree.pBt.pCursor; p != null; p = p.pNext )
      {
        int i;
        sqlite3BtreeClearCursor( p );
        p.eState = CURSOR_FAULT;
        p.skipNext = errCode;
        for ( i = 0; i <= p.iPage; i++ )
        {
          releasePage( p.apPage[i] );
          p.apPage[i] = null;
        }
      }
      sqlite3BtreeLeave( pBtree );
    }

    /*
    ** Rollback the transaction in progress.  All cursors will be
    ** invalided by this operation.  Any attempt to use a cursor
    ** that was open at the beginning of this operation will result
    ** in an error.
    **
    ** This will release the write lock on the database file.  If there
    ** are no active cursors, it also releases the read lock.
    */
    static int sqlite3BtreeRollback( Btree p )
    {
      int rc;
      BtShared pBt = p.pBt;
      MemPage pPage1 = new MemPage();

      sqlite3BtreeEnter( p );
      rc = saveAllCursors( pBt, 0, null );
#if !SQLITE_OMIT_SHARED_CACHE
if( rc!=SQLITE_OK ){
/* This is a horrible situation. An IO or malloc() error occurred whilst
** trying to save cursor positions. If this is an automatic rollback (as
** the result of a constraint, malloc() failure or IO error) then
** the cache may be internally inconsistent (not contain valid trees) so
** we cannot simply return the error to the caller. Instead, abort
** all queries that may be using any of the cursors that failed to save.
*/
sqlite3BtreeTripAllCursors(p, rc);
}
#endif
      btreeIntegrity( p );

      if ( p.inTrans == TRANS_WRITE )
      {
        int rc2;

        Debug.Assert( TRANS_WRITE == pBt.inTransaction );
        rc2 = sqlite3PagerRollback( pBt.pPager );
        if ( rc2 != SQLITE_OK )
        {
          rc = rc2;
        }

        /* The rollback may have destroyed the pPage1.aData value.  So
        ** call btreeGetPage() on page 1 again to make
        ** sure pPage1.aData is set correctly. */
        if ( btreeGetPage( pBt, 1, ref pPage1, 0 ) == SQLITE_OK )
        {
          releasePage( pPage1 );
        }
        Debug.Assert( countWriteCursors( pBt ) == 0 );
        pBt.inTransaction = TRANS_READ;
      }

      btreeEndTransaction( p );
      sqlite3BtreeLeave( p );
      return rc;
    }

    /*
    ** Start a statement subtransaction. The subtransaction can can be rolled
    ** back independently of the main transaction. You must start a transaction
    ** before starting a subtransaction. The subtransaction is ended automatically
    ** if the main transaction commits or rolls back.
    **
    ** Statement subtransactions are used around individual SQL statements
    ** that are contained within a BEGIN...COMMIT block.  If a constraint
    ** error occurs within the statement, the effect of that one statement
    ** can be rolled back without having to rollback the entire transaction.
    **
    ** A statement sub-transaction is implemented as an anonymous savepoint. The
    ** value passed as the second parameter is the total number of savepoints,
    ** including the new anonymous savepoint, open on the B-Tree. i.e. if there
    ** are no active savepoints and no other statement-transactions open,
    ** iStatement is 1. This anonymous savepoint can be released or rolled back
    ** using the sqlite3BtreeSavepoint() function.
    */
    static int sqlite3BtreeBeginStmt( Btree p, int iStatement )
    {
      int rc;
      BtShared pBt = p.pBt;
      sqlite3BtreeEnter( p );
      Debug.Assert( p.inTrans == TRANS_WRITE );
      Debug.Assert( !pBt.readOnly );
      Debug.Assert( iStatement > 0 );
      Debug.Assert( iStatement > p.db.nSavepoint );
      if ( NEVER( p.inTrans != TRANS_WRITE || pBt.readOnly ) )
      {
        rc = SQLITE_INTERNAL;
      }
      else
      {
        Debug.Assert( pBt.inTransaction == TRANS_WRITE );
        /* At the pager level, a statement transaction is a savepoint with
        ** an index greater than all savepoints created explicitly using
        ** SQL statements. It is illegal to open, release or rollback any
        ** such savepoints while the statement transaction savepoint is active.
        */
        rc = sqlite3PagerOpenSavepoint( pBt.pPager, iStatement );
      }
      sqlite3BtreeLeave( p );
      return rc;
    }

    /*
    ** The second argument to this function, op, is always SAVEPOINT_ROLLBACK
    ** or SAVEPOINT_RELEASE. This function either releases or rolls back the
    ** savepoint identified by parameter iSavepoint, depending on the value
    ** of op.
    **
    ** Normally, iSavepoint is greater than or equal to zero. However, if op is
    ** SAVEPOINT_ROLLBACK, then iSavepoint may also be -1. In this case the
    ** contents of the entire transaction are rolled back. This is different
    ** from a normal transaction rollback, as no locks are released and the
    ** transaction remains open.
    */
    static int sqlite3BtreeSavepoint( Btree p, int op, int iSavepoint )
    {
      int rc = SQLITE_OK;
      if ( p != null && p.inTrans == TRANS_WRITE )
      {
        BtShared pBt = p.pBt;
        Debug.Assert( op == SAVEPOINT_RELEASE || op == SAVEPOINT_ROLLBACK );
        Debug.Assert( iSavepoint >= 0 || ( iSavepoint == -1 && op == SAVEPOINT_ROLLBACK ) );
        sqlite3BtreeEnter( p );
        rc = sqlite3PagerSavepoint( pBt.pPager, op, iSavepoint );
        if ( rc == SQLITE_OK )
        {
          rc = newDatabase( pBt );
        }
        sqlite3BtreeLeave( p );
      }
      return rc;
    }

    /*
    ** Create a new cursor for the BTree whose root is on the page
    ** iTable. If a read-only cursor is requested, it is assumed that
    ** the caller already has at least a read-only transaction open
    ** on the database already. If a write-cursor is requested, then
    ** the caller is assumed to have an open write transaction.
    **
    ** If wrFlag==null, then the cursor can only be used for reading.
    ** If wrFlag==1, then the cursor can be used for reading or for
    ** writing if other conditions for writing are also met.  These
    ** are the conditions that must be met in order for writing to
    ** be allowed:
    **
    ** 1:  The cursor must have been opened with wrFlag==1
    **
    ** 2:  Other database connections that share the same pager cache
    **     but which are not in the READ_UNCOMMITTED state may not have
    **     cursors open with wrFlag==null on the same table.  Otherwise
    **     the changes made by this write cursor would be visible to
    **     the read cursors in the other database connection.
    **
    ** 3:  The database must be writable (not on read-only media)
    **
    ** 4:  There must be an active transaction.
    **
    ** No checking is done to make sure that page iTable really is the
    ** root page of a b-tree.  If it is not, then the cursor acquired
    ** will not work correctly.
    **
    ** It is assumed that the sqlite3BtreeCursorZero() has been called
    ** on pCur to initialize the memory space prior to invoking this routine.
    */
    static int btreeCursor(
    Btree p,                              /* The btree */
    int iTable,                           /* Root page of table to open */
    int wrFlag,                           /* 1 to write. 0 read-only */
    KeyInfo pKeyInfo,                     /* First arg to comparison function */
    BtCursor pCur                         /* Space for new cursor */
    )
    {
      BtShared pBt = p.pBt;                 /* Shared b-tree handle */

      Debug.Assert( sqlite3BtreeHoldsMutex( p ) );
      Debug.Assert( wrFlag == 0 || wrFlag == 1 );

      /* The following Debug.Assert statements verify that if this is a sharable
      ** b-tree database, the connection is holding the required table locks,
      ** and that no other connection has any open cursor that conflicts with
      ** this lock.  */
      Debug.Assert( hasSharedCacheTableLock( p, (u32)iTable, pKeyInfo != null ? 1 : 0, wrFlag + 1 ) );
      Debug.Assert( wrFlag == 0 || !hasReadConflicts( p, (u32)iTable ) );

      /* Assert that the caller has opened the required transaction. */
      Debug.Assert( p.inTrans > TRANS_NONE );
      Debug.Assert( wrFlag == 0 || p.inTrans == TRANS_WRITE );
      Debug.Assert( pBt.pPage1 != null && pBt.pPage1.aData != null );

      if ( NEVER( wrFlag != 0 && pBt.readOnly ) )
      {
        return SQLITE_READONLY;
      }
      if ( iTable == 1 && pagerPagecount( pBt ) == 0 )
      {
        return SQLITE_EMPTY;
      }

      /* Now that no other errors can occur, finish filling in the BtCursor
      ** variables and link the cursor into the BtShared list.  */
      pCur.pgnoRoot = (Pgno)iTable;
      pCur.iPage = -1;
      pCur.pKeyInfo = pKeyInfo;
      pCur.pBtree = p;
      pCur.pBt = pBt;
      pCur.wrFlag = (u8)wrFlag;
      pCur.pNext = pBt.pCursor;
      if ( pCur.pNext != null )
      {
        pCur.pNext.pPrev = pCur;
      }
      pBt.pCursor = pCur;
      pCur.eState = CURSOR_INVALID;
      pCur.cachedRowid = 0;
      return SQLITE_OK;
    }
    static int sqlite3BtreeCursor(
    Btree p,                                   /* The btree */
    int iTable,                                /* Root page of table to open */
    int wrFlag,                                /* 1 to write. 0 read-only */
    KeyInfo pKeyInfo,                          /* First arg to xCompare() */
    BtCursor pCur                              /* Write new cursor here */
    )
    {
      int rc;
      sqlite3BtreeEnter( p );
      rc = btreeCursor( p, iTable, wrFlag, pKeyInfo, pCur );
      sqlite3BtreeLeave( p );
      return rc;
    }

    /*
    ** Return the size of a BtCursor object in bytes.
    **
    ** This interfaces is needed so that users of cursors can preallocate
    ** sufficient storage to hold a cursor.  The BtCursor object is opaque
    ** to users so they cannot do the sizeof() themselves - they must call
    ** this routine.
    */
    static int sqlite3BtreeCursorSize()
    {
      return -1; // Not Used --  return ROUND8(sizeof(BtCursor));
    }

    /*
    ** Initialize memory that will be converted into a BtCursor object.
    **
    ** The simple approach here would be to memset() the entire object
    ** to zero.  But it turns out that the apPage[] and aiIdx[] arrays
    ** do not need to be zeroed and they are large, so we can save a lot
    ** of run-time by skipping the initialization of those elements.
    */
    static void sqlite3BtreeCursorZero( BtCursor p )
    {
      p.Clear(); // memset( p, 0, offsetof( BtCursor, iPage ) );
    }

    /*
    ** Set the cached rowid value of every cursor in the same database file
    ** as pCur and having the same root page number as pCur.  The value is
    ** set to iRowid.
    **
    ** Only positive rowid values are considered valid for this cache.
    ** The cache is initialized to zero, indicating an invalid cache.
    ** A btree will work fine with zero or negative rowids.  We just cannot
    ** cache zero or negative rowids, which means tables that use zero or
    ** negative rowids might run a little slower.  But in practice, zero
    ** or negative rowids are very uncommon so this should not be a problem.
    */
    static void sqlite3BtreeSetCachedRowid( BtCursor pCur, sqlite3_int64 iRowid )
    {
      BtCursor p;
      for ( p = pCur.pBt.pCursor; p != null; p = p.pNext )
      {
        if ( p.pgnoRoot == pCur.pgnoRoot ) p.cachedRowid = iRowid;
      }
      Debug.Assert( pCur.cachedRowid == iRowid );
    }

    /*
    ** Return the cached rowid for the given cursor.  A negative or zero
    ** return value indicates that the rowid cache is invalid and should be
    ** ignored.  If the rowid cache has never before been set, then a
    ** zero is returned.
    */
    static sqlite3_int64 sqlite3BtreeGetCachedRowid( BtCursor pCur )
    {
      return pCur.cachedRowid;
    }

    /*
    ** Close a cursor.  The read lock on the database file is released
    ** when the last cursor is closed.
    */
    static int sqlite3BtreeCloseCursor( BtCursor pCur )
    {
      Btree pBtree = pCur.pBtree;
      if ( pBtree != null )
      {
        int i;
        BtShared pBt = pCur.pBt;
        sqlite3BtreeEnter( pBtree );
        sqlite3BtreeClearCursor( pCur );
        if ( pCur.pPrev != null )
        {
          pCur.pPrev.pNext = pCur.pNext;
        }
        else
        {
          pBt.pCursor = pCur.pNext;
        }
        if ( pCur.pNext != null )
        {
          pCur.pNext.pPrev = pCur.pPrev;
        }
        for ( i = 0; i <= pCur.iPage; i++ )
        {
          releasePage( pCur.apPage[i] );
        }
        unlockBtreeIfUnused( pBt );
        invalidateOverflowCache( pCur );
        /* sqlite3_free(ref pCur); */
        sqlite3BtreeLeave( pBtree );
      }
      return SQLITE_OK;
    }

    /*
    ** Make sure the BtCursor* given in the argument has a valid
    ** BtCursor.info structure.  If it is not already valid, call
    ** btreeParseCell() to fill it in.
    **
    ** BtCursor.info is a cache of the information in the current cell.
    ** Using this cache reduces the number of calls to btreeParseCell().
    **
    ** 2007-06-25:  There is a bug in some versions of MSVC that cause the
    ** compiler to crash when getCellInfo() is implemented as a macro.
    ** But there is a measureable speed advantage to using the macro on gcc
    ** (when less compiler optimizations like -Os or -O0 are used and the
    ** compiler is not doing agressive inlining.)  So we use a real function
    ** for MSVC and a macro for everything else.  Ticket #2457.
    */
#if !NDEBUG
    static void assertCellInfo( BtCursor pCur )
    {
      CellInfo info;
      int iPage = pCur.iPage;
      info = new CellInfo();//memset(info, 0, sizeof(info));
      btreeParseCell( pCur.apPage[iPage], pCur.aiIdx[iPage], ref info );
      Debug.Assert( info.GetHashCode() == pCur.info.GetHashCode() || info.Equals( pCur.info ) );//memcmp(info, pCur.info, sizeof(info))==0 );
    }
#else
//  #define assertCellInfo(x)
static void assertCellInfo(BtCursor pCur) { }
#endif
#if _MSC_VER
    /* Use a real function in MSVC to work around bugs in that compiler. */
    static void getCellInfo( BtCursor pCur )
    {
      if ( pCur.info.nSize == 0 )
      {
        int iPage = pCur.iPage;
        btreeParseCell( pCur.apPage[iPage], pCur.aiIdx[iPage], ref pCur.info );
        pCur.validNKey = true;
      }
      else
      {
        assertCellInfo( pCur );
      }
    }
#else //* if not _MSC_VER */
/* Use a macro in all other compilers so that the function is inlined */
//#define getCellInfo(pCur)                                                      \
//  if( pCur.info.nSize==null ){                                                   \
//    int iPage = pCur.iPage;                                                   \
//    btreeParseCell(pCur.apPage[iPage],pCur.aiIdx[iPage],&pCur.info); \
//    pCur.validNKey = true;                                                       \
//  }else{                                                                       \
//    assertCellInfo(pCur);                                                      \
//  }
#endif //* _MSC_VER */

#if !NDEBUG  //* The next routine used only within Debug.Assert() statements */
    /*
** Return true if the given BtCursor is valid.  A valid cursor is one
** that is currently pointing to a row in a (non-empty) table.
** This is a verification routine is used only within Debug.Assert() statements.
*/
    static bool sqlite3BtreeCursorIsValid( BtCursor pCur )
    {
      return pCur != null && pCur.eState == CURSOR_VALID;
    }
#else
static bool sqlite3BtreeCursorIsValid(BtCursor pCur) { return true; }
#endif //* NDEBUG */

    /*
** Set pSize to the size of the buffer needed to hold the value of
** the key for the current entry.  If the cursor is not pointing
** to a valid entry, pSize is set to 0.
**
** For a table with the INTKEY flag set, this routine returns the key
** itself, not the number of bytes in the key.
**
** The caller must position the cursor prior to invoking this routine.
**
** This routine cannot fail.  It always returns SQLITE_OK.
*/
    static int sqlite3BtreeKeySize( BtCursor pCur, ref i64 pSize )
    {
      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( pCur.eState == CURSOR_INVALID || pCur.eState == CURSOR_VALID );
      if ( pCur.eState != CURSOR_VALID )
      {
        pSize = 0;
      }
      else
      {
        getCellInfo( pCur );
        pSize = pCur.info.nKey;
      }
      return SQLITE_OK;
    }

    /*
    ** Set pSize to the number of bytes of data in the entry the
    ** cursor currently points to.
    **
    ** The caller must guarantee that the cursor is pointing to a non-NULL
    ** valid entry.  In other words, the calling procedure must guarantee
    ** that the cursor has Cursor.eState==CURSOR_VALID.
    **
    ** Failure is not possible.  This function always returns SQLITE_OK.
    ** It might just as well be a procedure (returning void) but we continue
    ** to return an integer result code for historical reasons.
    */
    static int sqlite3BtreeDataSize( BtCursor pCur, ref u32 pSize )
    {
      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( pCur.eState == CURSOR_VALID );
      getCellInfo( pCur );
      pSize = pCur.info.nData;
      return SQLITE_OK;
    }

    /*
    ** Given the page number of an overflow page in the database (parameter
    ** ovfl), this function finds the page number of the next page in the
    ** linked list of overflow pages. If possible, it uses the auto-vacuum
    ** pointer-map data instead of reading the content of page ovfl to do so.
    **
    ** If an error occurs an SQLite error code is returned. Otherwise:
    **
    ** The page number of the next overflow page in the linked list is
    ** written to pPgnoNext. If page ovfl is the last page in its linked
    ** list, pPgnoNext is set to zero.
    **
    ** If ppPage is not NULL, and a reference to the MemPage object corresponding
    ** to page number pOvfl was obtained, then ppPage is set to point to that
    ** reference. It is the responsibility of the caller to call releasePage()
    ** on ppPage to free the reference. In no reference was obtained (because
    ** the pointer-map was used to obtain the value for pPgnoNext), then
    ** ppPage is set to zero.
    */
    static int getOverflowPage(
    BtShared pBt,               /* The database file */
    Pgno ovfl,                  /* Current overflow page number */
    ref MemPage ppPage,         /* OUT: MemPage handle (may be NULL) */
    ref Pgno pPgnoNext          /* OUT: Next overflow page number */
    )
    {
      Pgno next = 0;
      MemPage pPage = null;
      int rc = SQLITE_OK;

      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      // Debug.Assert( pPgnoNext);

#if !SQLITE_OMIT_AUTOVACUUM
      /* Try to find the next page in the overflow list using the
** autovacuum pointer-map pages. Guess that the next page in
** the overflow list is page number (ovfl+1). If that guess turns
** out to be wrong, fall back to loading the data of page
** number ovfl to determine the next page number.
*/
      if ( pBt.autoVacuum )
      {
        Pgno pgno = 0;
        Pgno iGuess = ovfl + 1;
        u8 eType = 0;

        while ( PTRMAP_ISPAGE( pBt, iGuess ) || iGuess == PENDING_BYTE_PAGE( pBt ) )
        {
          iGuess++;
        }

        if ( iGuess <= pagerPagecount( pBt ) )
        {
          rc = ptrmapGet( pBt, iGuess, ref eType, ref pgno );
          if ( rc == SQLITE_OK && eType == PTRMAP_OVERFLOW2 && pgno == ovfl )
          {
            next = iGuess;
            rc = SQLITE_DONE;
          }
        }
      }
#endif

      Debug.Assert( next == 0 || rc == SQLITE_DONE );
      if ( rc == SQLITE_OK )
      {
        rc = btreeGetPage( pBt, ovfl, ref pPage, 0 );
        Debug.Assert( rc == SQLITE_OK || pPage == null );
        if ( rc == SQLITE_OK )
        {
          next = sqlite3Get4byte( pPage.aData );
        }
      }

      pPgnoNext = next;
      if ( ppPage != null )
      {
        ppPage = pPage;
      }
      else
      {
        releasePage( pPage );
      }
      return ( rc == SQLITE_DONE ? SQLITE_OK : rc );
    }

    /*
    ** Copy data from a buffer to a page, or from a page to a buffer.
    **
    ** pPayload is a pointer to data stored on database page pDbPage.
    ** If argument eOp is false, then nByte bytes of data are copied
    ** from pPayload to the buffer pointed at by pBuf. If eOp is true,
    ** then sqlite3PagerWrite() is called on pDbPage and nByte bytes
    ** of data are copied from the buffer pBuf to pPayload.
    **
    ** SQLITE_OK is returned on success, otherwise an error code.
    */
    static int copyPayload(
    byte[] pPayload,           /* Pointer to page data */
    u32 payloadOffset,         /* Offset into page data */
    byte[] pBuf,               /* Pointer to buffer */
    u32 pBufOffset,            /* Offset into buffer */
    u32 nByte,                 /* Number of bytes to copy */
    int eOp,                   /* 0 . copy from page, 1 . copy to page */
    DbPage pDbPage             /* Page containing pPayload */
    )
    {
      if ( eOp != 0 )
      {
        /* Copy data from buffer to page (a write operation) */
        int rc = sqlite3PagerWrite( pDbPage );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
        Buffer.BlockCopy( pBuf, (int)pBufOffset, pPayload, (int)payloadOffset, (int)nByte );// memcpy( pPayload, pBuf, nByte );
      }
      else
      {
        /* Copy data from page to buffer (a read operation) */
        Buffer.BlockCopy( pPayload, (int)payloadOffset, pBuf, (int)pBufOffset, (int)nByte );//memcpy(pBuf, pPayload, nByte);
      }
      return SQLITE_OK;
    }
    //static int copyPayload(
    //  byte[] pPayload,           /* Pointer to page data */
    //  byte[] pBuf,               /* Pointer to buffer */
    //  int nByte,                 /* Number of bytes to copy */
    //  int eOp,                   /* 0 -> copy from page, 1 -> copy to page */
    //  DbPage pDbPage             /* Page containing pPayload */
    //){
    //  if( eOp!=0 ){
    //    /* Copy data from buffer to page (a write operation) */
    //    int rc = sqlite3PagerWrite(pDbPage);
    //    if( rc!=SQLITE_OK ){
    //      return rc;
    //    }
    //    memcpy(pPayload, pBuf, nByte);
    //  }else{
    //    /* Copy data from page to buffer (a read operation) */
    //    memcpy(pBuf, pPayload, nByte);
    //  }
    //  return SQLITE_OK;
    //}

    /*
    ** This function is used to read or overwrite payload information
    ** for the entry that the pCur cursor is pointing to. If the eOp
    ** parameter is 0, this is a read operation (data copied into
    ** buffer pBuf). If it is non-zero, a write (data copied from
    ** buffer pBuf).
    **
    ** A total of "amt" bytes are read or written beginning at "offset".
    ** Data is read to or from the buffer pBuf.
    **
    ** The content being read or written might appear on the main page
    ** or be scattered out on multiple overflow pages.
    **
    ** If the BtCursor.isIncrblobHandle flag is set, and the current
    ** cursor entry uses one or more overflow pages, this function
    ** allocates space for and lazily popluates the overflow page-list
    ** cache array (BtCursor.aOverflow). Subsequent calls use this
    ** cache to make seeking to the supplied offset more efficient.
    **
    ** Once an overflow page-list cache has been allocated, it may be
    ** invalidated if some other cursor writes to the same table, or if
    ** the cursor is moved to a different row. Additionally, in auto-vacuum
    ** mode, the following events may invalidate an overflow page-list cache.
    **
    **   * An incremental vacuum,
    **   * A commit in auto_vacuum="full" mode,
    **   * Creating a table (may require moving an overflow page).
    */
    static int accessPayload(
    BtCursor pCur,      /* Cursor pointing to entry to read from */
    u32 offset,         /* Begin reading this far into payload */
    u32 amt,            /* Read this many bytes */
    byte[] pBuf,        /* Write the bytes into this buffer */
    int eOp             /* zero to read. non-zero to write. */
    )
    {
      u32 pBufOffset = 0;
      byte[] aPayload;
      int rc = SQLITE_OK;
      u32 nKey;
      int iIdx = 0;
      MemPage pPage = pCur.apPage[pCur.iPage]; /* Btree page of current entry */
      BtShared pBt = pCur.pBt;                  /* Btree this cursor belongs to */

      Debug.Assert( pPage != null );
      Debug.Assert( pCur.eState == CURSOR_VALID );
      Debug.Assert( pCur.aiIdx[pCur.iPage] < pPage.nCell );
      Debug.Assert( cursorHoldsMutex( pCur ) );

      getCellInfo( pCur );
      aPayload = pCur.info.pCell; //pCur.info.pCell + pCur.info.nHeader;
      nKey = (u32)( pPage.intKey != 0 ? 0 : (int)pCur.info.nKey );

      if ( NEVER( offset + amt > nKey + pCur.info.nData )
      || pCur.info.nLocal > pBt.usableSize//&aPayload[pCur.info.nLocal] > &pPage.aData[pBt.usableSize]
      )
      {
        /* Trying to read or write past the end of the data is an error */
        return SQLITE_CORRUPT_BKPT();
      }

      /* Check if data must be read/written to/from the btree page itself. */
      if ( offset < pCur.info.nLocal )
      {
        int a = (int)amt;
        if ( a + offset > pCur.info.nLocal )
        {
          a = (int)( pCur.info.nLocal - offset );
        }
        rc = copyPayload( aPayload, (u32)( offset + pCur.info.iCell + pCur.info.nHeader ), pBuf, pBufOffset, (u32)a, eOp, pPage.pDbPage );
        offset = 0;
        pBufOffset += (u32)a; //pBuf += a;
        amt -= (u32)a;
      }
      else
      {
        offset -= pCur.info.nLocal;
      }

      if ( rc == SQLITE_OK && amt > 0 )
      {
        u32 ovflSize = (u32)( pBt.usableSize - 4 );  /* Bytes content per ovfl page */
        Pgno nextPage;

        nextPage = sqlite3Get4byte( aPayload, pCur.info.nLocal + pCur.info.iCell + pCur.info.nHeader );

#if !SQLITE_OMIT_INCRBLOB
/* If the isIncrblobHandle flag is set and the BtCursor.aOverflow[]
** has not been allocated, allocate it now. The array is sized at
** one entry for each overflow page in the overflow chain. The
** page number of the first overflow page is stored in aOverflow[0],
** etc. A value of 0 in the aOverflow[] array means "not yet known"
** (the cache is lazily populated).
*/
if( pCur.isIncrblobHandle && !pCur.aOverflow ){
int nOvfl = (pCur.info.nPayload-pCur.info.nLocal+ovflSize-1)/ovflSize;
pCur.aOverflow = (Pgno *)sqlite3MallocZero(sizeof(Pgno)*nOvfl);
/* nOvfl is always positive.  If it were zero, fetchPayload would have
** been used instead of this routine. */
if( ALWAYS(nOvfl) && !pCur.aOverflow ){
rc = SQLITE_NOMEM;
}
}

/* If the overflow page-list cache has been allocated and the
** entry for the first required overflow page is valid, skip
** directly to it.
*/
if( pCur.aOverflow && pCur.aOverflow[offset/ovflSize] ){
iIdx = (offset/ovflSize);
nextPage = pCur.aOverflow[iIdx];
offset = (offset%ovflSize);
}
#endif

        for ( ; rc == SQLITE_OK && amt > 0 && nextPage != 0; iIdx++ )
        {

#if !SQLITE_OMIT_INCRBLOB
/* If required, populate the overflow page-list cache. */
if( pCur.aOverflow ){
Debug.Assert(!pCur.aOverflow[iIdx] || pCur.aOverflow[iIdx]==nextPage);
pCur.aOverflow[iIdx] = nextPage;
}
#endif

          MemPage MemPageDummy = null;
          if ( offset >= ovflSize )
          {
            /* The only reason to read this page is to obtain the page
            ** number for the next page in the overflow chain. The page
            ** data is not required. So first try to lookup the overflow
            ** page-list cache, if any, then fall back to the getOverflowPage()
            ** function.
            */
#if !SQLITE_OMIT_INCRBLOB
if( pCur.aOverflow && pCur.aOverflow[iIdx+1] ){
nextPage = pCur.aOverflow[iIdx+1];
} else
#endif
            rc = getOverflowPage( pBt, nextPage, ref  MemPageDummy, ref nextPage );
            offset -= ovflSize;
          }
          else
          {
            /* Need to read this page properly. It contains some of the
            ** range of data that is being read (eOp==null) or written (eOp!=null).
            */
            DbPage pDbPage = new PgHdr();
            int a = (int)amt;
            rc = sqlite3PagerGet( pBt.pPager, nextPage, ref pDbPage );
            if ( rc == SQLITE_OK )
            {
              aPayload = sqlite3PagerGetData( pDbPage );
              nextPage = sqlite3Get4byte( aPayload );
              if ( a + offset > ovflSize )
              {
                a = (int)( ovflSize - offset );
              }
              rc = copyPayload( aPayload, offset + 4, pBuf, pBufOffset, (u32)a, eOp, pDbPage );
              sqlite3PagerUnref( pDbPage );
              offset = 0;
              amt -= (u32)a;
              pBufOffset += (u32)a;//pBuf += a;
            }
          }
        }
      }

      if ( rc == SQLITE_OK && amt > 0 )
      {
        return SQLITE_CORRUPT_BKPT();
      }
      return rc;
    }

    /*
    ** Read part of the key associated with cursor pCur.  Exactly
    ** "amt" bytes will be transfered into pBuf[].  The transfer
    ** begins at "offset".
    **
    ** The caller must ensure that pCur is pointing to a valid row
    ** in the table.
    **
    ** Return SQLITE_OK on success or an error code if anything goes
    ** wrong.  An error is returned if "offset+amt" is larger than
    ** the available payload.
    */
    static int sqlite3BtreeKey( BtCursor pCur, u32 offset, u32 amt, byte[] pBuf )
    {
      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( pCur.eState == CURSOR_VALID );
      Debug.Assert( pCur.iPage >= 0 && pCur.apPage[pCur.iPage] != null );
      Debug.Assert(pCur.aiIdx[pCur.iPage] < pCur.apPage[pCur.iPage].nCell);
      return accessPayload( pCur, offset, amt, pBuf, 0 );
    }

    /*
    ** Read part of the data associated with cursor pCur.  Exactly
    ** "amt" bytes will be transfered into pBuf[].  The transfer
    ** begins at "offset".
    **
    ** Return SQLITE_OK on success or an error code if anything goes
    ** wrong.  An error is returned if "offset+amt" is larger than
    ** the available payload.
    */
    static int sqlite3BtreeData( BtCursor pCur, u32 offset, u32 amt, byte[] pBuf )
    {
      int rc;

#if !SQLITE_OMIT_INCRBLOB
if ( pCur.eState==CURSOR_INVALID ){
return SQLITE_ABORT;
}
#endif

      Debug.Assert( cursorHoldsMutex( pCur ) );
      rc = restoreCursorPosition( pCur );
      if ( rc == SQLITE_OK )
      {
        Debug.Assert( pCur.eState == CURSOR_VALID );
        Debug.Assert( pCur.iPage >= 0 && pCur.apPage[pCur.iPage] != null );
        Debug.Assert( pCur.aiIdx[pCur.iPage] < pCur.apPage[pCur.iPage].nCell );
        rc = accessPayload( pCur, offset, amt, pBuf, 0 );
      }
      return rc;
    }

    /*
    ** Return a pointer to payload information from the entry that the
    ** pCur cursor is pointing to.  The pointer is to the beginning of
    ** the key if skipKey==null and it points to the beginning of data if
    ** skipKey==1.  The number of bytes of available key/data is written
    ** into pAmt.  If pAmt==null, then the value returned will not be
    ** a valid pointer.
    **
    ** This routine is an optimization.  It is common for the entire key
    ** and data to fit on the local page and for there to be no overflow
    ** pages.  When that is so, this routine can be used to access the
    ** key and data without making a copy.  If the key and/or data spills
    ** onto overflow pages, then accessPayload() must be used to reassemble
    ** the key/data and copy it into a preallocated buffer.
    **
    ** The pointer returned by this routine looks directly into the cached
    ** page of the database.  The data might change or move the next time
    ** any btree routine is called.
    */
    static byte[] fetchPayload(
    BtCursor pCur,   /* Cursor pointing to entry to read from */
    ref int pAmt,    /* Write the number of available bytes here */
    ref int outOffset, /* Offset into Buffer */
    bool skipKey    /* read beginning at data if this is true */
    )
    {
      byte[] aPayload;
      MemPage pPage;
      u32 nKey;
      u32 nLocal;

      Debug.Assert( pCur != null && pCur.iPage >= 0 && pCur.apPage[pCur.iPage] != null );
      Debug.Assert( pCur.eState == CURSOR_VALID );
      Debug.Assert( cursorHoldsMutex( pCur ) );
      outOffset = -1;
      pPage = pCur.apPage[pCur.iPage];
      Debug.Assert( pCur.aiIdx[pCur.iPage] < pPage.nCell );
      if ( NEVER( pCur.info.nSize == 0 ) )
      {
        btreeParseCell( pCur.apPage[pCur.iPage], pCur.aiIdx[pCur.iPage],
        ref pCur.info );
      }
      //aPayload = pCur.info.pCell;
      //aPayload += pCur.info.nHeader;
      aPayload = sqlite3Malloc(pCur.info.nSize - pCur.info.nHeader);
      if ( pPage.intKey != 0 )
      {
        nKey = 0;
      }
      else
      {
        nKey = (u32)pCur.info.nKey;
      }
      if ( skipKey )
      {
        //aPayload += nKey;
        outOffset = (int)( pCur.info.iCell + pCur.info.nHeader + nKey );
        Buffer.BlockCopy( pCur.info.pCell, outOffset, aPayload, 0, (int)( pCur.info.nSize - pCur.info.nHeader - nKey ) );
        nLocal = pCur.info.nLocal - nKey;
      }
      else
      {
        outOffset = (int)( pCur.info.iCell + pCur.info.nHeader );
        Buffer.BlockCopy( pCur.info.pCell, outOffset, aPayload, 0, pCur.info.nSize - pCur.info.nHeader );
        nLocal = pCur.info.nLocal;
        Debug.Assert( nLocal <= nKey );
      }
      pAmt = (int)nLocal;
      return aPayload;
    }

    /*
    ** For the entry that cursor pCur is point to, return as
    ** many bytes of the key or data as are available on the local
    ** b-tree page.  Write the number of available bytes into pAmt.
    **
    ** The pointer returned is ephemeral.  The key/data may move
    ** or be destroyed on the next call to any Btree routine,
    ** including calls from other threads against the same cache.
    ** Hence, a mutex on the BtShared should be held prior to calling
    ** this routine.
    **
    ** These routines is used to get quick access to key and data
    ** in the common case where no overflow pages are used.
    */
    static byte[] sqlite3BtreeKeyFetch( BtCursor pCur, ref int pAmt, ref int outOffset )
    {
      byte[] p = null;
      Debug.Assert( sqlite3_mutex_held( pCur.pBtree.db.mutex ) );
      Debug.Assert( cursorHoldsMutex( pCur ) );
      if ( ALWAYS( pCur.eState == CURSOR_VALID ) )
      {
        p = fetchPayload( pCur, ref pAmt, ref outOffset, false );
      }
      return p;
    }
    static byte[] sqlite3BtreeDataFetch( BtCursor pCur, ref int pAmt, ref int outOffset )
    {
      byte[] p = null;
      Debug.Assert( sqlite3_mutex_held( pCur.pBtree.db.mutex ) );
      Debug.Assert( cursorHoldsMutex( pCur ) );
      if ( ALWAYS( pCur.eState == CURSOR_VALID ) )
      {
        p = fetchPayload( pCur, ref pAmt, ref outOffset, true );
      }
      return p;
    }

    /*
    ** Move the cursor down to a new child page.  The newPgno argument is the
    ** page number of the child page to move to.
    **
    ** This function returns SQLITE_CORRUPT if the page-header flags field of
    ** the new child page does not match the flags field of the parent (i.e.
    ** if an intkey page appears to be the parent of a non-intkey page, or
    ** vice-versa).
    */
    static int moveToChild( BtCursor pCur, u32 newPgno )
    {
      int rc;
      int i = pCur.iPage;
      MemPage pNewPage = new MemPage();
      BtShared pBt = pCur.pBt;

      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( pCur.eState == CURSOR_VALID );
      Debug.Assert( pCur.iPage < BTCURSOR_MAX_DEPTH );
      if ( pCur.iPage >= ( BTCURSOR_MAX_DEPTH - 1 ) )
      {
        return SQLITE_CORRUPT_BKPT();
      }
      rc = getAndInitPage( pBt, newPgno, ref pNewPage );
      if ( rc != 0 ) return rc;
      pCur.apPage[i + 1] = pNewPage;
      pCur.aiIdx[i + 1] = 0;
      pCur.iPage++;

      pCur.info.nSize = 0;
      pCur.validNKey = false;
      if ( pNewPage.nCell < 1 || pNewPage.intKey != pCur.apPage[i].intKey )
      {
        return SQLITE_CORRUPT_BKPT();
      }
      return SQLITE_OK;
    }

#if !NDEBUG
    /*
** Page pParent is an internal (non-leaf) tree page. This function
** asserts that page number iChild is the left-child if the iIdx'th
** cell in page pParent. Or, if iIdx is equal to the total number of
** cells in pParent, that page number iChild is the right-child of
** the page.
*/
    static void assertParentIndex( MemPage pParent, int iIdx, Pgno iChild )
    {
      Debug.Assert( iIdx <= pParent.nCell );
      if ( iIdx == pParent.nCell )
      {
        Debug.Assert( sqlite3Get4byte( pParent.aData, pParent.hdrOffset + 8 ) == iChild );
      }
      else
      {
        Debug.Assert( sqlite3Get4byte( pParent.aData, findCell( pParent, iIdx ) ) == iChild );
      }
    }
#else
//#  define assertParentIndex(x,y,z)
static void assertParentIndex(MemPage pParent, int iIdx, Pgno iChild) { }
#endif

    /*
** Move the cursor up to the parent page.
**
** pCur.idx is set to the cell index that contains the pointer
** to the page we are coming from.  If we are coming from the
** right-most child page then pCur.idx is set to one more than
** the largest cell index.
*/
    static void moveToParent( BtCursor pCur )
    {
      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( pCur.eState == CURSOR_VALID );
      Debug.Assert( pCur.iPage > 0 );
      Debug.Assert( pCur.apPage[pCur.iPage] != null );
      assertParentIndex(
      pCur.apPage[pCur.iPage - 1],
      pCur.aiIdx[pCur.iPage - 1],
      pCur.apPage[pCur.iPage].pgno
      );
      releasePage( pCur.apPage[pCur.iPage] );
      pCur.iPage--;
      pCur.info.nSize = 0;
      pCur.validNKey = false;
    }

    /*
    ** Move the cursor to point to the root page of its b-tree structure.
    **
    ** If the table has a virtual root page, then the cursor is moved to point
    ** to the virtual root page instead of the actual root page. A table has a
    ** virtual root page when the actual root page contains no cells and a
    ** single child page. This can only happen with the table rooted at page 1.
    **
    ** If the b-tree structure is empty, the cursor state is set to
    ** CURSOR_INVALID. Otherwise, the cursor is set to point to the first
    ** cell located on the root (or virtual root) page and the cursor state
    ** is set to CURSOR_VALID.
    **
    ** If this function returns successfully, it may be assumed that the
    ** page-header flags indicate that the [virtual] root-page is the expected
    ** kind of b-tree page (i.e. if when opening the cursor the caller did not
    ** specify a KeyInfo structure the flags byte is set to 0x05 or 0x0D,
    ** indicating a table b-tree, or if the caller did specify a KeyInfo
    ** structure the flags byte is set to 0x02 or 0x0A, indicating an index
    ** b-tree).
    */
    static int moveToRoot( BtCursor pCur )
    {
      MemPage pRoot;
      int rc = SQLITE_OK;
      Btree p = pCur.pBtree;
      BtShared pBt = p.pBt;

      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( CURSOR_INVALID < CURSOR_REQUIRESEEK );
      Debug.Assert( CURSOR_VALID < CURSOR_REQUIRESEEK );
      Debug.Assert( CURSOR_FAULT > CURSOR_REQUIRESEEK );
      if ( pCur.eState >= CURSOR_REQUIRESEEK )
      {
        if ( pCur.eState == CURSOR_FAULT )
        {
          Debug.Assert( pCur.skipNext != SQLITE_OK );
          return pCur.skipNext;
        }
        sqlite3BtreeClearCursor( pCur );
      }

      if ( pCur.iPage >= 0 )
      {
        int i;
        for ( i = 1; i <= pCur.iPage; i++ )
        {
          releasePage( pCur.apPage[i] );
        }
        pCur.iPage = 0;
      }
      else
      {
        rc = getAndInitPage( pBt, pCur.pgnoRoot, ref pCur.apPage[0] );
        if ( rc != SQLITE_OK )
        {
          pCur.eState = CURSOR_INVALID;
          return rc;
        }
        pCur.iPage = 0;

        /* If pCur.pKeyInfo is not NULL, then the caller that opened this cursor
        ** expected to open it on an index b-tree. Otherwise, if pKeyInfo is
        ** NULL, the caller expects a table b-tree. If this is not the case,
        ** return an SQLITE_CORRUPT error.  */
        Debug.Assert( pCur.apPage[0].intKey == 1 || pCur.apPage[0].intKey == 0 );
        if ( ( pCur.pKeyInfo == null ) != ( pCur.apPage[0].intKey != 0 ) )
        {
          return SQLITE_CORRUPT_BKPT();
        }
      }

      /* Assert that the root page is of the correct type. This must be the
      ** case as the call to this function that loaded the root-page (either
      ** this call or a previous invocation) would have detected corruption
      ** if the assumption were not true, and it is not possible for the flags
      ** byte to have been modified while this cursor is holding a reference
      ** to the page.  */
      pRoot = pCur.apPage[0];
      Debug.Assert( pRoot.pgno == pCur.pgnoRoot );
      Debug.Assert( pRoot.isInit != 0 && ( pCur.pKeyInfo == null ) == ( pRoot.intKey != 0 ) );

      pCur.aiIdx[0] = 0;
      pCur.info.nSize = 0;
      pCur.atLast = 0;
      pCur.validNKey = false;

      if ( pRoot.nCell == 0 && 0 == pRoot.leaf )
      {
        Pgno subpage;
        if ( pRoot.pgno != 1 )
          return SQLITE_CORRUPT_BKPT();
        subpage = sqlite3Get4byte( pRoot.aData, pRoot.hdrOffset + 8 );
        pCur.eState = CURSOR_VALID;
        rc = moveToChild( pCur, subpage );
      }
      else
      {
        pCur.eState = ( ( pRoot.nCell > 0 ) ? CURSOR_VALID : CURSOR_INVALID );
      }
      return rc;
    }

    /*
    ** Move the cursor down to the left-most leaf entry beneath the
    ** entry to which it is currently pointing.
    **
    ** The left-most leaf is the one with the smallest key - the first
    ** in ascending order.
    */
    static int moveToLeftmost( BtCursor pCur )
    {
      Pgno pgno;
      int rc = SQLITE_OK;
      MemPage pPage;

      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( pCur.eState == CURSOR_VALID );
      while ( rc == SQLITE_OK && 0 == ( pPage = pCur.apPage[pCur.iPage] ).leaf )
      {
        Debug.Assert( pCur.aiIdx[pCur.iPage] < pPage.nCell );
        pgno = sqlite3Get4byte( pPage.aData, findCell( pPage, pCur.aiIdx[pCur.iPage] ) );
        rc = moveToChild( pCur, pgno );
      }
      return rc;
    }

    /*
    ** Move the cursor down to the right-most leaf entry beneath the
    ** page to which it is currently pointing.  Notice the difference
    ** between moveToLeftmost() and moveToRightmost().  moveToLeftmost()
    ** finds the left-most entry beneath the *entry* whereas moveToRightmost()
    ** finds the right-most entry beneath the page*.
    **
    ** The right-most entry is the one with the largest key - the last
    ** key in ascending order.
    */
    static int moveToRightmost( BtCursor pCur )
    {
      Pgno pgno;
      int rc = SQLITE_OK;
      MemPage pPage = null;

      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( pCur.eState == CURSOR_VALID );
      while ( rc == SQLITE_OK && 0 == ( pPage = pCur.apPage[pCur.iPage] ).leaf )
      {
        pgno = sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 );
        pCur.aiIdx[pCur.iPage] = pPage.nCell;
        rc = moveToChild( pCur, pgno );
      }
      if ( rc == SQLITE_OK )
      {
        pCur.aiIdx[pCur.iPage] = (u16)( pPage.nCell - 1 );
        pCur.info.nSize = 0;
        pCur.validNKey = false;
      }
      return rc;
    }

    /* Move the cursor to the first entry in the table.  Return SQLITE_OK
    ** on success.  Set pRes to 0 if the cursor actually points to something
    ** or set pRes to 1 if the table is empty.
    */
    static int sqlite3BtreeFirst( BtCursor pCur, ref int pRes )
    {
      int rc;

      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( sqlite3_mutex_held( pCur.pBtree.db.mutex ) );
      rc = moveToRoot( pCur );
      if ( rc == SQLITE_OK )
      {
        if ( pCur.eState == CURSOR_INVALID )
        {
          Debug.Assert( pCur.apPage[pCur.iPage].nCell == 0 );
          pRes = 1;
          rc = SQLITE_OK;
        }
        else
        {
          Debug.Assert( pCur.apPage[pCur.iPage].nCell > 0 );
          pRes = 0;
          rc = moveToLeftmost( pCur );
        }
      }
      return rc;
    }

    /* Move the cursor to the last entry in the table.  Return SQLITE_OK
    ** on success.  Set pRes to 0 if the cursor actually points to something
    ** or set pRes to 1 if the table is empty.
    */
    static int sqlite3BtreeLast( BtCursor pCur, ref int pRes )
    {
      int rc;

      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( sqlite3_mutex_held( pCur.pBtree.db.mutex ) );

      /* If the cursor already points to the last entry, this is a no-op. */
      if ( CURSOR_VALID == pCur.eState && pCur.atLast != 0 )
      {
#if SQLITE_DEBUG
        /* This block serves to Debug.Assert() that the cursor really does point
** to the last entry in the b-tree. */
        int ii;
        for ( ii = 0; ii < pCur.iPage; ii++ )
        {
          Debug.Assert( pCur.aiIdx[ii] == pCur.apPage[ii].nCell );
        }
        Debug.Assert( pCur.aiIdx[pCur.iPage] == pCur.apPage[pCur.iPage].nCell - 1 );
        Debug.Assert( pCur.apPage[pCur.iPage].leaf != 0 );
#endif
        return SQLITE_OK;
      }

      rc = moveToRoot( pCur );
      if ( rc == SQLITE_OK )
      {
        if ( CURSOR_INVALID == pCur.eState )
        {
          Debug.Assert( pCur.apPage[pCur.iPage].nCell == 0 );
          pRes = 1;
        }
        else
        {
          Debug.Assert( pCur.eState == CURSOR_VALID );
          pRes = 0;
          rc = moveToRightmost( pCur );
          pCur.atLast = (u8)( rc == SQLITE_OK ? 1 : 0 );
        }
      }
      return rc;
    }

    /* Move the cursor so that it points to an entry near the key
    ** specified by pIdxKey or intKey.   Return a success code.
    **
    ** For INTKEY tables, the intKey parameter is used.  pIdxKey
    ** must be NULL.  For index tables, pIdxKey is used and intKey
    ** is ignored.
    **
    ** If an exact match is not found, then the cursor is always
    ** left pointing at a leaf page which would hold the entry if it
    ** were present.  The cursor might point to an entry that comes
    ** before or after the key.
    **
    ** An integer is written into pRes which is the result of
    ** comparing the key with the entry to which the cursor is
    ** pointing.  The meaning of the integer written into
    ** pRes is as follows:
    **
    **     pRes<0      The cursor is left pointing at an entry that
    **                  is smaller than intKey/pIdxKey or if the table is empty
    **                  and the cursor is therefore left point to nothing.
    **
    **     pRes==null     The cursor is left pointing at an entry that
    **                  exactly matches intKey/pIdxKey.
    **
    **     pRes>0      The cursor is left pointing at an entry that
    **                  is larger than intKey/pIdxKey.
    **
    */
    static int sqlite3BtreeMovetoUnpacked(
    BtCursor pCur,           /* The cursor to be moved */
    UnpackedRecord pIdxKey,  /* Unpacked index key */
    i64 intKey,              /* The table key */
    int biasRight,           /* If true, bias the search to the high end */
    ref int pRes             /* Write search results here */
    )
    {
      int rc;

      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( sqlite3_mutex_held( pCur.pBtree.db.mutex ) );
      // Not needed in C# // Debug.Assert( pRes != 0 );
      Debug.Assert( ( pIdxKey == null ) == ( pCur.pKeyInfo == null ) );

      /* If the cursor is already positioned at the point we are trying
      ** to move to, then just return without doing any work */
      if ( pCur.eState == CURSOR_VALID && pCur.validNKey
      && pCur.apPage[0].intKey != 0
      )
      {
        if ( pCur.info.nKey == intKey )
        {
          pRes = 0;
          return SQLITE_OK;
        }
        if ( pCur.atLast != 0 && pCur.info.nKey < intKey )
        {
          pRes = -1;
          return SQLITE_OK;
        }
      }

      rc = moveToRoot( pCur );
      if ( rc != 0 )
      {
        return rc;
      }
      Debug.Assert( pCur.apPage[pCur.iPage] != null );
      Debug.Assert( pCur.apPage[pCur.iPage].isInit != 0 );
      Debug.Assert( pCur.apPage[pCur.iPage].nCell > 0 || pCur.eState == CURSOR_INVALID );
      if ( pCur.eState == CURSOR_INVALID )
      {
        pRes = -1;
        Debug.Assert( pCur.apPage[pCur.iPage].nCell == 0 );
        return SQLITE_OK;
      }
      Debug.Assert( pCur.apPage[0].intKey != 0 || pIdxKey != null );
      for ( ; ; )
      {
        int lwr, upr;
        Pgno chldPg;
        MemPage pPage = pCur.apPage[pCur.iPage];
        int c;

        /* pPage.nCell must be greater than zero. If this is the root-page
        ** the cursor would have been INVALID above and this for(;;) loop
        ** not run. If this is not the root-page, then the moveToChild() routine
        ** would have already detected db corruption. Similarly, pPage must
        ** be the right kind (index or table) of b-tree page. Otherwise
        ** a moveToChild() or moveToRoot() call would have detected corruption.  */
        Debug.Assert( pPage.nCell > 0 );
        Debug.Assert( pPage.intKey == ( ( pIdxKey == null ) ? 1 : 0 ) );
        lwr = 0;
        upr = pPage.nCell - 1;
        if ( biasRight != 0 )
        {
          pCur.aiIdx[pCur.iPage] = (u16)upr;
        }
        else
        {
          pCur.aiIdx[pCur.iPage] = (u16)( ( upr + lwr ) / 2 );
        }
        for ( ; ; )
        {
          int idx = pCur.aiIdx[pCur.iPage]; /* Index of current cell in pPage */
          int pCell;                        /* Pointer to current cell in pPage */

          pCur.info.nSize = 0;
          pCell = findCell( pPage, idx ) + pPage.childPtrSize;
          if ( pPage.intKey != 0 )
          {
            i64 nCellKey = 0;
            if ( pPage.hasData != 0 )
            {
              u32 Dummy0 = 0;
              pCell += getVarint32( pPage.aData, pCell, ref Dummy0 );
            }
            getVarint( pPage.aData, pCell, ref nCellKey );
            if ( nCellKey == intKey )
            {
              c = 0;
            }
            else if ( nCellKey < intKey )
            {
              c = -1;
            }
            else
            {
              Debug.Assert( nCellKey > intKey );
              c = +1;
            }
            pCur.validNKey = true;
            pCur.info.nKey = nCellKey;
          }
          else
          {
            /* The maximum supported page-size is 32768 bytes. This means that
            ** the maximum number of record bytes stored on an index B-Tree
            ** page is at most 8198 bytes, which may be stored as a 2-byte
            ** varint. This information is used to attempt to avoid parsing
            ** the entire cell by checking for the cases where the record is
            ** stored entirely within the b-tree page by inspecting the first
            ** 2 bytes of the cell.
            */
            int nCell = pPage.aData[pCell + 0]; //pCell[0];
            if ( 0 == ( nCell & 0x80 ) && nCell <= pPage.maxLocal )
            {
              /* This branch runs if the record-size field of the cell is a
              ** single byte varint and the record fits entirely on the main
              ** b-tree page.  */
              c = sqlite3VdbeRecordCompare( nCell, pPage.aData, pCell + 1, pIdxKey ); //c = sqlite3VdbeRecordCompare( nCell, (void*)&pCell[1], pIdxKey );
            }
            else if ( 0 == ( pPage.aData[pCell + 1] & 0x80 )//!(pCell[1] & 0x80)
            && ( nCell = ( ( nCell & 0x7f ) << 7 ) + pPage.aData[pCell + 1] ) <= pPage.maxLocal//pCell[1])<=pPage.maxLocal
            )
            {
              /* The record-size field is a 2 byte varint and the record
              ** fits entirely on the main b-tree page.  */
              c = sqlite3VdbeRecordCompare( nCell, pPage.aData, pCell + 2, pIdxKey ); //c = sqlite3VdbeRecordCompare( nCell, (void*)&pCell[2], pIdxKey );
            }
            else
            {
              /* The record flows over onto one or more overflow pages. In
              ** this case the whole cell needs to be parsed, a buffer allocated
              ** and accessPayload() used to retrieve the record into the
              ** buffer before VdbeRecordCompare() can be called. */
              u8[] pCellKey;
              u8[] pCellBody = new u8[pPage.aData.Length - pCell + pPage.childPtrSize];
              Buffer.BlockCopy( pPage.aData, pCell - pPage.childPtrSize, pCellBody, 0, pCellBody.Length );//          u8 * const pCellBody = pCell - pPage->childPtrSize;
              btreeParseCellPtr( pPage, pCellBody, ref pCur.info );
              nCell = (int)pCur.info.nKey;
              pCellKey = sqlite3Malloc( nCell );
              //if ( pCellKey == null )
              //{
              //  rc = SQLITE_NOMEM;
              //  goto moveto_finish;
              //}
              rc = accessPayload( pCur, 0, (u32)nCell, pCellKey, 0 );
              if ( rc != 0 )
              {
                pCellKey = null;// sqlite3_free(ref pCellKey );
                goto moveto_finish;
              }
              c = sqlite3VdbeRecordCompare( nCell, pCellKey, pIdxKey );
              pCellKey = null;// sqlite3_free(ref pCellKey );
            }
          }
          if ( c == 0 )
          {
            if ( pPage.intKey != 0 && 0 == pPage.leaf )
            {
              lwr = idx;
              upr = lwr - 1;
              break;
            }
            else
            {
              pRes = 0;
              rc = SQLITE_OK;
              goto moveto_finish;
            }
          }
          if ( c < 0 )
          {
            lwr = idx + 1;
          }
          else
          {
            upr = idx - 1;
          }
          if ( lwr > upr )
          {
            break;
          }
          pCur.aiIdx[pCur.iPage] = (u16)( ( lwr + upr ) / 2 );
        }
        Debug.Assert( lwr == upr + 1 );
        Debug.Assert( pPage.isInit != 0 );
        if ( pPage.leaf != 0 )
        {
          chldPg = 0;
        }
        else if ( lwr >= pPage.nCell )
        {
          chldPg = sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 );
        }
        else
        {
          chldPg = sqlite3Get4byte( pPage.aData, findCell( pPage, lwr ) );
        }
        if ( chldPg == 0 )
        {
          Debug.Assert( pCur.aiIdx[pCur.iPage] < pCur.apPage[pCur.iPage].nCell );
          pRes = c;
          rc = SQLITE_OK;
          goto moveto_finish;
        }
        pCur.aiIdx[pCur.iPage] = (u16)lwr;
        pCur.info.nSize = 0;
        pCur.validNKey = false;
        rc = moveToChild( pCur, chldPg );
        if ( rc != 0 ) goto moveto_finish;
      }
    moveto_finish:
      return rc;
    }


    /*
    ** Return TRUE if the cursor is not pointing at an entry of the table.
    **
    ** TRUE will be returned after a call to sqlite3BtreeNext() moves
    ** past the last entry in the table or sqlite3BtreePrev() moves past
    ** the first entry.  TRUE is also returned if the table is empty.
    */
    static bool sqlite3BtreeEof( BtCursor pCur )
    {
      /* TODO: What if the cursor is in CURSOR_REQUIRESEEK but all table entries
      ** have been deleted? This API will need to change to return an error code
      ** as well as the boolean result value.
      */
      return ( CURSOR_VALID != pCur.eState );
    }

    /*
    ** Advance the cursor to the next entry in the database.  If
    ** successful then set pRes=0.  If the cursor
    ** was already pointing to the last entry in the database before
    ** this routine was called, then set pRes=1.
    */
    static int sqlite3BtreeNext( BtCursor pCur, ref int pRes )
    {
      int rc;
      int idx;
      MemPage pPage;

      Debug.Assert( cursorHoldsMutex( pCur ) );
      rc = restoreCursorPosition( pCur );
      if ( rc != SQLITE_OK )
      {
        return rc;
      }
      // Not needed in C# // Debug.Assert( pRes != 0 );
      if ( CURSOR_INVALID == pCur.eState )
      {
        pRes = 1;
        return SQLITE_OK;
      }
      if ( pCur.skipNext > 0 )
      {
        pCur.skipNext = 0;
        pRes = 0;
        return SQLITE_OK;
      }
      pCur.skipNext = 0;

      pPage = pCur.apPage[pCur.iPage];
      idx = ++pCur.aiIdx[pCur.iPage];
      Debug.Assert( pPage.isInit != 0 );
      Debug.Assert( idx <= pPage.nCell );

      pCur.info.nSize = 0;
      pCur.validNKey = false;
      if ( idx >= pPage.nCell )
      {
        if ( 0 == pPage.leaf )
        {
          rc = moveToChild( pCur, sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 ) );
          if ( rc != 0 ) return rc;
          rc = moveToLeftmost( pCur );
          pRes = 0;
          return rc;
        }
        do
        {
          if ( pCur.iPage == 0 )
          {
            pRes = 1;
            pCur.eState = CURSOR_INVALID;
            return SQLITE_OK;
          }
          moveToParent( pCur );
          pPage = pCur.apPage[pCur.iPage];
        } while ( pCur.aiIdx[pCur.iPage] >= pPage.nCell );
        pRes = 0;
        if ( pPage.intKey != 0 )
        {
          rc = sqlite3BtreeNext( pCur, ref pRes );
        }
        else
        {
          rc = SQLITE_OK;
        }
        return rc;
      }
      pRes = 0;
      if ( pPage.leaf != 0 )
      {
        return SQLITE_OK;
      }
      rc = moveToLeftmost( pCur );
      return rc;
    }


    /*
    ** Step the cursor to the back to the previous entry in the database.  If
    ** successful then set pRes=0.  If the cursor
    ** was already pointing to the first entry in the database before
    ** this routine was called, then set pRes=1.
    */
    static int sqlite3BtreePrevious( BtCursor pCur, ref int pRes )
    {
      int rc;
      MemPage pPage;

      Debug.Assert( cursorHoldsMutex( pCur ) );
      rc = restoreCursorPosition( pCur );
      if ( rc != SQLITE_OK )
      {
        return rc;
      }
      pCur.atLast = 0;
      if ( CURSOR_INVALID == pCur.eState )
      {
        pRes = 1;
        return SQLITE_OK;
      }
      if ( pCur.skipNext < 0 )
      {
        pCur.skipNext = 0;
        pRes = 0;
        return SQLITE_OK;
      }
      pCur.skipNext = 0;

      pPage = pCur.apPage[pCur.iPage];
      Debug.Assert( pPage.isInit != 0 );
      if ( 0 == pPage.leaf )
      {
        int idx = pCur.aiIdx[pCur.iPage];
        rc = moveToChild( pCur, sqlite3Get4byte( pPage.aData, findCell( pPage, idx ) ) );
        if ( rc != 0 )
        {
          return rc;
        }
        rc = moveToRightmost( pCur );
      }
      else
      {
        while ( pCur.aiIdx[pCur.iPage] == 0 )
        {
          if ( pCur.iPage == 0 )
          {
            pCur.eState = CURSOR_INVALID;
            pRes = 1;
            return SQLITE_OK;
          }
          moveToParent( pCur );
        }
        pCur.info.nSize = 0;
        pCur.validNKey = false;

        pCur.aiIdx[pCur.iPage]--;
        pPage = pCur.apPage[pCur.iPage];
        if ( pPage.intKey != 0 && 0 == pPage.leaf )
        {
          rc = sqlite3BtreePrevious( pCur, ref pRes );
        }
        else
        {
          rc = SQLITE_OK;
        }
      }
      pRes = 0;
      return rc;
    }

    /*
    ** Allocate a new page from the database file.
    **
    ** The new page is marked as dirty.  (In other words, sqlite3PagerWrite()
    ** has already been called on the new page.)  The new page has also
    ** been referenced and the calling routine is responsible for calling
    ** sqlite3PagerUnref() on the new page when it is done.
    **
    ** SQLITE_OK is returned on success.  Any other return value indicates
    ** an error.  ppPage and pPgno are undefined in the event of an error.
    ** Do not invoke sqlite3PagerUnref() on ppPage if an error is returned.
    **
    ** If the "nearby" parameter is not 0, then a (feeble) effort is made to
    ** locate a page close to the page number "nearby".  This can be used in an
    ** attempt to keep related pages close to each other in the database file,
    ** which in turn can make database access faster.
    **
    ** If the "exact" parameter is not 0, and the page-number nearby exists
    ** anywhere on the free-list, then it is guarenteed to be returned. This
    ** is only used by auto-vacuum databases when allocating a new table.
    */
    static int allocateBtreePage(
    BtShared pBt,
    ref MemPage ppPage,
    ref Pgno pPgno,
    Pgno nearby,
    u8 exact
    )
    {
      MemPage pPage1;
      int rc;
      u32 n;     /* Number of pages on the freelist */
      u32 k;     /* Number of leaves on the trunk of the freelist */
      MemPage pTrunk = null;
      MemPage pPrevTrunk = null;
      Pgno mxPage;     /* Total size of the database file */

      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      pPage1 = pBt.pPage1;
      mxPage = pagerPagecount( pBt );
      n = sqlite3Get4byte( pPage1.aData, 36 );
      testcase( n == mxPage - 1 );
      if ( n >= mxPage )
      {
        return SQLITE_CORRUPT_BKPT();
      }
      if ( n > 0 )
      {
        /* There are pages on the freelist.  Reuse one of those pages. */
        Pgno iTrunk;
        u8 searchList = 0; /* If the free-list must be searched for 'nearby' */

        /* If the 'exact' parameter was true and a query of the pointer-map
        ** shows that the page 'nearby' is somewhere on the free-list, then
        ** the entire-list will be searched for that page.
        */
#if !SQLITE_OMIT_AUTOVACUUM
        if ( exact != 0 && nearby <= mxPage )
        {
          u8 eType = 0;
          Debug.Assert( nearby > 0 );
          Debug.Assert( pBt.autoVacuum );
          u32 Dummy0 = 0; rc = ptrmapGet( pBt, nearby, ref eType, ref Dummy0 );
          if ( rc != 0 ) return rc;
          if ( eType == PTRMAP_FREEPAGE )
          {
            searchList = 1;
          }
          pPgno = nearby;
        }
#endif

        /* Decrement the free-list count by 1. Set iTrunk to the index of the
** first free-list trunk page. iPrevTrunk is initially 1.
*/
        rc = sqlite3PagerWrite( pPage1.pDbPage );
        if ( rc != 0 ) return rc;
        sqlite3Put4byte( pPage1.aData, (u32)36, n - 1 );

        /* The code within this loop is run only once if the 'searchList' variable
        ** is not true. Otherwise, it runs once for each trunk-page on the
        ** free-list until the page 'nearby' is located.
        */
        do
        {
          pPrevTrunk = pTrunk;
          if ( pPrevTrunk != null )
          {
            iTrunk = sqlite3Get4byte( pPrevTrunk.aData, 0 );
          }
          else
          {
            iTrunk = sqlite3Get4byte( pPage1.aData, 32 );
          }
          testcase( iTrunk == mxPage );
          if ( iTrunk > mxPage )
          {
            rc = SQLITE_CORRUPT_BKPT();
          }
          else
          {
            rc = btreeGetPage( pBt, iTrunk, ref pTrunk, 0 );
          }
          if ( rc != 0 )
          {
            pTrunk = null;
            goto end_allocate_page;
          }

          k = sqlite3Get4byte( pTrunk.aData, 4 );
          if ( k == 0 && 0 == searchList )
          {
            /* The trunk has no leaves and the list is not being searched.
            ** So extract the trunk page itself and use it as the newly
            ** allocated page */
            Debug.Assert( pPrevTrunk == null );
            rc = sqlite3PagerWrite( pTrunk.pDbPage );
            if ( rc != 0 )
            {
              goto end_allocate_page;
            }
            pPgno = iTrunk;
            Buffer.BlockCopy( pTrunk.aData, 0, pPage1.aData, 32, 4 );//memcpy( pPage1.aData[32], ref pTrunk.aData[0], 4 );
            ppPage = pTrunk;
            pTrunk = null;
            TRACE( "ALLOCATE: %d trunk - %d free pages left\n", pPgno, n - 1 );
          }
          else if ( k > (u32)( pBt.usableSize / 4 - 2 ) )
          {
            /* Value of k is out of range.  Database corruption */
            rc = SQLITE_CORRUPT_BKPT();
            goto end_allocate_page;
#if !SQLITE_OMIT_AUTOVACUUM
          }
          else if ( searchList != 0 && nearby == iTrunk )
          {
            /* The list is being searched and this trunk page is the page
            ** to allocate, regardless of whether it has leaves.
            */
            Debug.Assert( pPgno == iTrunk );
            ppPage = pTrunk;
            searchList = 0;
            rc = sqlite3PagerWrite( pTrunk.pDbPage );
            if ( rc != 0 )
            {
              goto end_allocate_page;
            }
            if ( k == 0 )
            {
              if ( null == pPrevTrunk )
              {
                //memcpy(pPage1.aData[32], pTrunk.aData[0], 4);
                pPage1.aData[32 + 0] = pTrunk.aData[0 + 0];
                pPage1.aData[32 + 1] = pTrunk.aData[0 + 1];
                pPage1.aData[32 + 2] = pTrunk.aData[0 + 2];
                pPage1.aData[32 + 3] = pTrunk.aData[0 + 3];
              }
              else
              {
                //memcpy(pPrevTrunk.aData[0], pTrunk.aData[0], 4);
                pPrevTrunk.aData[0 + 0] = pTrunk.aData[0 + 0];
                pPrevTrunk.aData[0 + 1] = pTrunk.aData[0 + 1];
                pPrevTrunk.aData[0 + 2] = pTrunk.aData[0 + 2];
                pPrevTrunk.aData[0 + 3] = pTrunk.aData[0 + 3];
              }
            }
            else
            {
              /* The trunk page is required by the caller but it contains
              ** pointers to free-list leaves. The first leaf becomes a trunk
              ** page in this case.
              */
              MemPage pNewTrunk = new MemPage();
              Pgno iNewTrunk = sqlite3Get4byte( pTrunk.aData, 8 );
              if ( iNewTrunk > mxPage )
              {
                rc = SQLITE_CORRUPT_BKPT();
                goto end_allocate_page;
              }
              testcase( iNewTrunk == mxPage );
              rc = btreeGetPage( pBt, iNewTrunk, ref pNewTrunk, 0 );
              if ( rc != SQLITE_OK )
              {
                goto end_allocate_page;
              }
              rc = sqlite3PagerWrite( pNewTrunk.pDbPage );
              if ( rc != SQLITE_OK )
              {
                releasePage( pNewTrunk );
                goto end_allocate_page;
              }
              //memcpy(pNewTrunk.aData[0], pTrunk.aData[0], 4);
              pNewTrunk.aData[0 + 0] = pTrunk.aData[0 + 0];
              pNewTrunk.aData[0 + 1] = pTrunk.aData[0 + 1];
              pNewTrunk.aData[0 + 2] = pTrunk.aData[0 + 2];
              pNewTrunk.aData[0 + 3] = pTrunk.aData[0 + 3];
              sqlite3Put4byte( pNewTrunk.aData, (u32)4, (u32)( k - 1 ) );
              Buffer.BlockCopy( pTrunk.aData, 12, pNewTrunk.aData, 8, (int)( k - 1 ) * 4 );//memcpy( pNewTrunk.aData[8], ref pTrunk.aData[12], ( k - 1 ) * 4 );
              releasePage( pNewTrunk );
              if ( null == pPrevTrunk )
              {
                Debug.Assert( sqlite3PagerIswriteable( pPage1.pDbPage ) );
                sqlite3Put4byte( pPage1.aData, (u32)32, iNewTrunk );
              }
              else
              {
                rc = sqlite3PagerWrite( pPrevTrunk.pDbPage );
                if ( rc != 0 )
                {
                  goto end_allocate_page;
                }
                sqlite3Put4byte( pPrevTrunk.aData, (u32)0, iNewTrunk );
              }
            }
            pTrunk = null;
            TRACE( "ALLOCATE: %d trunk - %d free pages left\n", pPgno, n - 1 );
#endif
          }
          else if ( k > 0 )
          {
            /* Extract a leaf from the trunk */
            u32 closest;
            Pgno iPage;
            byte[] aData = pTrunk.aData;
            rc = sqlite3PagerWrite( pTrunk.pDbPage );
            if ( rc != 0 )
            {
              goto end_allocate_page;
            }
            if ( nearby > 0 )
            {
              u32 i;
              int dist;
              closest = 0;
              dist = (int)( sqlite3Get4byte( aData, 8 ) - nearby );
              if ( dist < 0 ) dist = -dist;
              for ( i = 1; i < k; i++ )
              {
                int d2 = (int)( sqlite3Get4byte( aData, 8 + i * 4 ) - nearby );
                if ( d2 < 0 ) d2 = -d2;
                if ( d2 < dist )
                {
                  closest = i;
                  dist = d2;
                }
              }
            }
            else
            {
              closest = 0;
            }

            iPage = sqlite3Get4byte( aData, 8 + closest * 4 );
            testcase( iPage == mxPage );
            if ( iPage > mxPage )
            {
              rc = SQLITE_CORRUPT_BKPT();
              goto end_allocate_page;
            }
            testcase( iPage == mxPage );
            if ( 0 == searchList || iPage == nearby )
            {
              int noContent;
              pPgno = iPage;
              TRACE( "ALLOCATE: %d was leaf %d of %d on trunk %d" +
              ": %d more free pages\n",
              pPgno, closest + 1, k, pTrunk.pgno, n - 1 );
              if ( closest < k - 1 )
              {
                Buffer.BlockCopy( aData, (int)( 4 + k * 4 ), aData, 8 + (int)closest * 4, 4 );//memcpy( aData[8 + closest * 4], ref aData[4 + k * 4], 4 );
              }
              sqlite3Put4byte( aData, (u32)4, ( k - 1 ) );// sqlite3Put4byte( aData, 4, k - 1 );
              Debug.Assert( sqlite3PagerIswriteable( pTrunk.pDbPage ) );
              noContent = !btreeGetHasContent( pBt, pPgno ) ? 1 : 0;
              rc = btreeGetPage( pBt, pPgno, ref ppPage, noContent );
              if ( rc == SQLITE_OK )
              {
                rc = sqlite3PagerWrite( ( ppPage ).pDbPage );
                if ( rc != SQLITE_OK )
                {
                  releasePage( ppPage );
                }
              }
              searchList = 0;
            }
          }
          releasePage( pPrevTrunk );
          pPrevTrunk = null;
        } while ( searchList != 0 );
      }
      else
      {
        /* There are no pages on the freelist, so create a new page at the
        ** end of the file */
        int nPage = (int)pagerPagecount( pBt );
        pPgno = (u32)nPage + 1;

        if ( pPgno == PENDING_BYTE_PAGE( pBt ) )
        {
          ( pPgno )++;
        }

#if !SQLITE_OMIT_AUTOVACUUM
        if ( pBt.autoVacuum && PTRMAP_ISPAGE( pBt, pPgno ) )
        {
          /* If pPgno refers to a pointer-map page, allocate two new pages
          ** at the end of the file instead of one. The first allocated page
          ** becomes a new pointer-map page, the second is used by the caller.
          */
          MemPage pPg = null;
          TRACE( "ALLOCATE: %d from end of file (pointer-map page)\n", pPgno );
          Debug.Assert( pPgno != PENDING_BYTE_PAGE( pBt ) );
          rc = btreeGetPage( pBt, pPgno, ref pPg, 0 );
          if ( rc == SQLITE_OK )
          {
            rc = sqlite3PagerWrite( pPg.pDbPage );
            releasePage( pPg );
          }
          if ( rc != 0 ) return rc;
          ( pPgno )++;
          if ( pPgno == PENDING_BYTE_PAGE( pBt ) ) { ( pPgno )++; }
        }
#endif

        Debug.Assert( pPgno != PENDING_BYTE_PAGE( pBt ) );
        rc = btreeGetPage( pBt, pPgno, ref ppPage, 0 );
        if ( rc != 0 ) return rc;
        rc = sqlite3PagerWrite( ( ppPage ).pDbPage );
        if ( rc != SQLITE_OK )
        {
          releasePage( ppPage );
        }
        TRACE( "ALLOCATE: %d from end of file\n", pPgno );
      }

      Debug.Assert( pPgno != PENDING_BYTE_PAGE( pBt ) );

    end_allocate_page:
      releasePage( pTrunk );
      releasePage( pPrevTrunk );
      if ( rc == SQLITE_OK )
      {
        if ( sqlite3PagerPageRefcount( ( ppPage ).pDbPage ) > 1 )
        {
          releasePage( ppPage );
          return SQLITE_CORRUPT_BKPT();
        }
        ( ppPage ).isInit = 0;
      }
      else
      {
        ppPage = null;
      }
      return rc;
    }

    /*
    ** This function is used to add page iPage to the database file free-list.
    ** It is assumed that the page is not already a part of the free-list.
    **
    ** The value passed as the second argument to this function is optional.
    ** If the caller happens to have a pointer to the MemPage object
    ** corresponding to page iPage handy, it may pass it as the second value.
    ** Otherwise, it may pass NULL.
    **
    ** If a pointer to a MemPage object is passed as the second argument,
    ** its reference count is not altered by this function.
    */
    static int freePage2( BtShared pBt, MemPage pMemPage, Pgno iPage )
    {
      MemPage pTrunk = null;                /* Free-list trunk page */
      Pgno iTrunk = 0;                    /* Page number of free-list trunk page */
      MemPage pPage1 = pBt.pPage1;      /* Local reference to page 1 */
      MemPage pPage;                     /* Page being freed. May be NULL. */
      int rc;                             /* Return Code */
      int nFree;                          /* Initial number of pages on free-list */

      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      Debug.Assert( iPage > 1 );
      Debug.Assert( null == pMemPage || pMemPage.pgno == iPage );

      if ( pMemPage != null )
      {
        pPage = pMemPage;
        sqlite3PagerRef( pPage.pDbPage );
      }
      else
      {
        pPage = btreePageLookup( pBt, iPage );
      }

      /* Increment the free page count on pPage1 */
      rc = sqlite3PagerWrite( pPage1.pDbPage );
      if ( rc != 0 ) goto freepage_out;
      nFree = (int)sqlite3Get4byte( pPage1.aData, 36 );
      sqlite3Put4byte( pPage1.aData, 36, nFree + 1 );

      if (pBt.secureDelete)
      {
        /* If the secure_delete option is enabled, then
        ** always fully overwrite deleted information with zeros.
        */
        if ((null==pPage && ((rc = btreeGetPage(pBt, iPage, ref pPage, 0)) != 0))
         || ((rc = sqlite3PagerWrite(pPage.pDbPage)) != 0)
        )
        {
          goto freepage_out;
        }
        Array.Clear(pPage.aData, 0, pPage.pBt.pageSize);//memset(pPage->aData, 0, pPage->pBt->pageSize);
      }

      /* If the database supports auto-vacuum, write an entry in the pointer-map
** to indicate that the page is free.
*/
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
      if ( pBt.autoVacuum )
#else
if (false)
#endif
      {
        ptrmapPut( pBt, iPage, PTRMAP_FREEPAGE, 0, ref rc );
        if ( rc != 0 ) goto freepage_out;
      }

      /* Now manipulate the actual database free-list structure. There are two
      ** possibilities. If the free-list is currently empty, or if the first
      ** trunk page in the free-list is full, then this page will become a
      ** new free-list trunk page. Otherwise, it will become a leaf of the
      ** first trunk page in the current free-list. This block tests if it
      ** is possible to add the page as a new free-list leaf.
      */
      if ( nFree != 0 )
      {
        u32 nLeaf;                /* Initial number of leaf cells on trunk page */

        iTrunk = sqlite3Get4byte( pPage1.aData, 32 );
        rc = btreeGetPage( pBt, iTrunk, ref pTrunk, 0 );
        if ( rc != SQLITE_OK )
        {
          goto freepage_out;
        }

        nLeaf = sqlite3Get4byte( pTrunk.aData, 4 );
        Debug.Assert( pBt.usableSize > 32 );
        if ( nLeaf > (u32)pBt.usableSize / 4 - 2 )
        {
          rc = SQLITE_CORRUPT_BKPT();
          goto freepage_out;
        }
        if ( nLeaf < (u32)pBt.usableSize / 4 - 8 )
        {
          /* In this case there is room on the trunk page to insert the page
          ** being freed as a new leaf.
          **
          ** Note that the trunk page is not really full until it contains
          ** usableSize/4 - 2 entries, not usableSize/4 - 8 entries as we have
          ** coded.  But due to a coding error in versions of SQLite prior to
          ** 3.6.0, databases with freelist trunk pages holding more than
          ** usableSize/4 - 8 entries will be reported as corrupt.  In order
          ** to maintain backwards compatibility with older versions of SQLite,
          ** we will continue to restrict the number of entries to usableSize/4 - 8
          ** for now.  At some point in the future (once everyone has upgraded
          ** to 3.6.0 or later) we should consider fixing the conditional above
          ** to read "usableSize/4-2" instead of "usableSize/4-8".
          */
          rc = sqlite3PagerWrite( pTrunk.pDbPage );
          if ( rc == SQLITE_OK )
          {
            sqlite3Put4byte( pTrunk.aData, (u32)4, nLeaf + 1 );
            sqlite3Put4byte( pTrunk.aData, (u32)8 + nLeaf * 4, iPage );
            if (pPage != null && !pBt.secureDelete)
            {
              sqlite3PagerDontWrite( pPage.pDbPage );
            }
            rc = btreeSetHasContent( pBt, iPage );
          }
          TRACE( "FREE-PAGE: %d leaf on trunk page %d\n", iPage, pTrunk.pgno );
          goto freepage_out;
        }
      }

      /* If control flows to this point, then it was not possible to add the
      ** the page being freed as a leaf page of the first trunk in the free-list.
      ** Possibly because the free-list is empty, or possibly because the
      ** first trunk in the free-list is full. Either way, the page being freed
      ** will become the new first trunk page in the free-list.
      */
      if ( pPage == null && SQLITE_OK != ( rc = btreeGetPage( pBt, iPage, ref pPage, 0 ) ) )
      {
        goto freepage_out;
      }
      rc = sqlite3PagerWrite( pPage.pDbPage );
      if ( rc != SQLITE_OK )
      {
        goto freepage_out;
      }
      sqlite3Put4byte( pPage.aData, iTrunk );
      sqlite3Put4byte( pPage.aData, 4, 0 );
      sqlite3Put4byte( pPage1.aData, (u32)32, iPage );
      TRACE( "FREE-PAGE: %d new trunk page replacing %d\n", pPage.pgno, iTrunk );

    freepage_out:
      if ( pPage != null )
      {
        pPage.isInit = 0;
      }
      releasePage( pPage );
      releasePage( pTrunk );
      return rc;
    }
    static void freePage( MemPage pPage, ref int pRC )
    {
      if ( ( pRC ) == SQLITE_OK )
      {
        pRC = freePage2( pPage.pBt, pPage, pPage.pgno );
      }
    }

    /*
    ** Free any overflow pages associated with the given Cell.
    */
    static int clearCell( MemPage pPage, int pCell )
    {
      BtShared pBt = pPage.pBt;
      CellInfo info = new CellInfo();
      Pgno ovflPgno;
      int rc;
      int nOvfl;
      u16 ovflPageSize;

      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      btreeParseCellPtr( pPage, pCell, ref info );
      if ( info.iOverflow == 0 )
      {
        return SQLITE_OK;  /* No overflow pages. Return without doing anything */
      }
      ovflPgno = sqlite3Get4byte( pPage.aData, pCell, info.iOverflow );
      Debug.Assert( pBt.usableSize > 4 );
      ovflPageSize = (u16)( pBt.usableSize - 4 );
      nOvfl = (int)( ( info.nPayload - info.nLocal + ovflPageSize - 1 ) / ovflPageSize );
      Debug.Assert( ovflPgno == 0 || nOvfl > 0 );
      while ( nOvfl-- != 0 )
      {
        Pgno iNext = 0;
        MemPage pOvfl = null;
        if ( ovflPgno < 2 || ovflPgno > pagerPagecount( pBt ) )
        {
          /* 0 is not a legal page number and page 1 cannot be an
          ** overflow page. Therefore if ovflPgno<2 or past the end of the
          ** file the database must be corrupt. */
          return SQLITE_CORRUPT_BKPT();
        }
        if ( nOvfl != 0 )
        {
          rc = getOverflowPage( pBt, ovflPgno, ref pOvfl, ref iNext );
          if ( rc != 0 ) return rc;
        }

        if ((pOvfl !=null || ((pOvfl = btreePageLookup(pBt, ovflPgno)) != null))
         && sqlite3PagerPageRefcount(pOvfl.pDbPage) != 1
        )
        {
          /* There is no reason any cursor should have an outstanding reference 
          ** to an overflow page belonging to a cell that is being deleted/updated.
          ** So if there exists more than one reference to this page, then it 
          ** must not really be an overflow page and the database must be corrupt. 
          ** It is helpful to detect this before calling freePage2(), as 
          ** freePage2() may zero the page contents if secure-delete mode is
          ** enabled. If this 'overflow' page happens to be a page that the
          ** caller is iterating through or using in some other way, this
          ** can be problematic.
          */
          rc = SQLITE_CORRUPT_BKPT();
        }
        else
        {
          rc = freePage2(pBt, pOvfl, ovflPgno);
        }
        if (pOvfl != null)
        {
          sqlite3PagerUnref( pOvfl.pDbPage );
        }
        if ( rc != 0 ) return rc;
        ovflPgno = iNext;
      }
      return SQLITE_OK;
    }

    /*
    ** Create the byte sequence used to represent a cell on page pPage
    ** and write that byte sequence into pCell[].  Overflow pages are
    ** allocated and filled in as necessary.  The calling procedure
    ** is responsible for making sure sufficient space has been allocated
    ** for pCell[].
    **
    ** Note that pCell does not necessary need to point to the pPage.aData
    ** area.  pCell might point to some temporary storage.  The cell will
    ** be constructed in this temporary area then copied into pPage.aData
    ** later.
    */
    static int fillInCell(
    MemPage pPage,            /* The page that contains the cell */
    byte[] pCell,             /* Complete text of the cell */
    byte[] pKey, i64 nKey,    /* The key */
    byte[] pData, int nData,  /* The data */
    int nZero,                /* Extra zero bytes to append to pData */
    ref int pnSize            /* Write cell size here */
    )
    {
      int nPayload;
      u8[] pSrc; int pSrcIndex = 0;
      int nSrc, n, rc;
      int spaceLeft;
      MemPage pOvfl = null;
      MemPage pToRelease = null;
      byte[] pPrior; int pPriorIndex = 0;
      byte[] pPayload; int pPayloadIndex = 0;
      BtShared pBt = pPage.pBt;
      Pgno pgnoOvfl = 0;
      int nHeader;
      CellInfo info = new CellInfo();

      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );

      /* pPage is not necessarily writeable since pCell might be auxiliary
      ** buffer space that is separate from the pPage buffer area */
      // TODO -- Determine if the following Assert is needed under c#
      //Debug.Assert( pCell < pPage.aData || pCell >= &pPage.aData[pBt.pageSize]
      //          || sqlite3PagerIswriteable(pPage.pDbPage) );

      /* Fill in the header. */
      nHeader = 0;
      if ( 0 == pPage.leaf )
      {
        nHeader += 4;
      }
      if ( pPage.hasData != 0 )
      {
        nHeader += (int)putVarint( pCell, nHeader, (int)( nData + nZero ) ); //putVarint( pCell[nHeader], nData + nZero );
      }
      else
      {
        nData = nZero = 0;
      }
      nHeader += putVarint( pCell, nHeader, (u64)nKey ); //putVarint( pCell[nHeader], *(u64*)&nKey );
      btreeParseCellPtr( pPage, pCell, ref info );
      Debug.Assert( info.nHeader == nHeader );
      Debug.Assert( info.nKey == nKey );
      Debug.Assert( info.nData == (u32)( nData + nZero ) );

      /* Fill in the payload */
      nPayload = nData + nZero;
      if ( pPage.intKey != 0 )
      {
        pSrc = pData;
        nSrc = nData;
        nData = 0;
      }
      else
      {
        if ( NEVER( nKey > 0x7fffffff || pKey == null ) )
        {
          return SQLITE_CORRUPT_BKPT();
        }
        nPayload += (int)nKey;
        pSrc = pKey;
        nSrc = (int)nKey;
      }
      pnSize = info.nSize;
      spaceLeft = info.nLocal;
      //  pPayload = &pCell[nHeader];
      pPayload = pCell;
      pPayloadIndex = nHeader;
      //  pPrior = &pCell[info.iOverflow];
      pPrior = pCell;
      pPriorIndex = info.iOverflow;

      while ( nPayload > 0 )
      {
        if ( spaceLeft == 0 )
        {
#if !SQLITE_OMIT_AUTOVACUUM
          Pgno pgnoPtrmap = pgnoOvfl; /* Overflow page pointer-map entry page */
          if ( pBt.autoVacuum )
          {
            do
            {
              pgnoOvfl++;
            } while (
            PTRMAP_ISPAGE( pBt, pgnoOvfl ) || pgnoOvfl == PENDING_BYTE_PAGE( pBt )
            );
          }
#endif
          rc = allocateBtreePage( pBt, ref pOvfl, ref pgnoOvfl, pgnoOvfl, 0 );
#if !SQLITE_OMIT_AUTOVACUUM
          /* If the database supports auto-vacuum, and the second or subsequent
** overflow page is being allocated, add an entry to the pointer-map
** for that page now.
**
** If this is the first overflow page, then write a partial entry
** to the pointer-map. If we write nothing to this pointer-map slot,
** then the optimistic overflow chain processing in clearCell()
** may misinterpret the uninitialised values and delete the
** wrong pages from the database.
*/
          if ( pBt.autoVacuum && rc == SQLITE_OK )
          {
            u8 eType = (u8)( pgnoPtrmap != 0 ? PTRMAP_OVERFLOW2 : PTRMAP_OVERFLOW1 );
            ptrmapPut( pBt, pgnoOvfl, eType, pgnoPtrmap, ref rc );
            if ( rc != 0 )
            {
              releasePage( pOvfl );
            }
          }
#endif
          if ( rc != 0 )
          {
            releasePage( pToRelease );
            return rc;
          }

          /* If pToRelease is not zero than pPrior points into the data area
          ** of pToRelease.  Make sure pToRelease is still writeable. */
          Debug.Assert( pToRelease == null || sqlite3PagerIswriteable( pToRelease.pDbPage ) );

          /* If pPrior is part of the data area of pPage, then make sure pPage
          ** is still writeable */
          // TODO -- Determine if the following Assert is needed under c#
          //Debug.Assert( pPrior < pPage.aData || pPrior >= &pPage.aData[pBt.pageSize]
          //      || sqlite3PagerIswriteable(pPage.pDbPage) );

          sqlite3Put4byte( pPrior, pPriorIndex, pgnoOvfl );
          releasePage( pToRelease );
          pToRelease = pOvfl;
          pPrior = pOvfl.aData; pPriorIndex = 0;
          sqlite3Put4byte( pPrior, 0 );
          pPayload = pOvfl.aData; pPayloadIndex = 4; //&pOvfl.aData[4];
          spaceLeft = pBt.usableSize - 4;
        }
        n = nPayload;
        if ( n > spaceLeft ) n = spaceLeft;

        /* If pToRelease is not zero than pPayload points into the data area
        ** of pToRelease.  Make sure pToRelease is still writeable. */
        Debug.Assert( pToRelease == null || sqlite3PagerIswriteable( pToRelease.pDbPage ) );

        /* If pPayload is part of the data area of pPage, then make sure pPage
        ** is still writeable */
        // TODO -- Determine if the following Assert is needed under c#
        //Debug.Assert( pPayload < pPage.aData || pPayload >= &pPage.aData[pBt.pageSize]
        //        || sqlite3PagerIswriteable(pPage.pDbPage) );

        if ( nSrc > 0 )
        {
          if ( n > nSrc ) n = nSrc;
          Debug.Assert( pSrc != null );
          Buffer.BlockCopy( pSrc, pSrcIndex, pPayload, pPayloadIndex, n );//memcpy(pPayload, pSrc, n);
        }
        else
        {
          byte[] pZeroBlob = sqlite3Malloc(n); // memset(pPayload, 0, n);
          Buffer.BlockCopy( pZeroBlob, 0, pPayload, pPayloadIndex, n );
        }
        nPayload -= n;
        pPayloadIndex += n;// pPayload += n;
        pSrcIndex += n;// pSrc += n;
        nSrc -= n;
        spaceLeft -= n;
        if ( nSrc == 0 )
        {
          nSrc = nData;
          pSrc = pData;
        }
      }
      releasePage( pToRelease );
      return SQLITE_OK;
    }

    /*
    ** Remove the i-th cell from pPage.  This routine effects pPage only.
    ** The cell content is not freed or deallocated.  It is assumed that
    ** the cell content has been copied someplace else.  This routine just
    ** removes the reference to the cell from pPage.
    **
    ** "sz" must be the number of bytes in the cell.
    */
    static void dropCell( MemPage pPage, int idx, int sz, ref int pRC )
    {
      int i;          /* Loop counter */
      int pc;         /* Offset to cell content of cell being deleted */
      u8[] data;      /* pPage.aData */
      int ptr;        /* Used to move bytes around within data[] */
      int rc;         /* The return code */
      int hdr;        /* Beginning of the header.  0 most pages.  100 page 1 */

      if ( pRC != 0 ) return;

      //Debug.Assert( idx >= 0 && idx < pPage.nCell );
      //Debug.Assert( sz == cellSize( pPage, idx ) );
      //Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
      //Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      data = pPage.aData;
      ptr = pPage.cellOffset + 2 * idx; //ptr = &data[pPage.cellOffset + 2 * idx];
      pc = get2byte( data, ptr );
      hdr = pPage.hdrOffset;
      testcase( pc == get2byte( data, hdr + 5 ) );
      testcase( pc + sz == pPage.pBt.usableSize );
      if ( pc < get2byte( data, hdr + 5 ) || pc + sz > pPage.pBt.usableSize )
      {
        pRC = SQLITE_CORRUPT_BKPT();
        return;
      }
      rc = freeSpace( pPage, pc, sz );
      if ( rc != 0 )
      {
        pRC = rc;
        return;
      }
      //for ( i = idx + 1 ; i < pPage.nCell ; i++, ptr += 2 )
      //{
      //  ptr[0] = ptr[2];
      //  ptr[1] = ptr[3];
      //}
      Buffer.BlockCopy( data, ptr + 2, data, ptr, ( pPage.nCell - 1 - idx ) * 2 );
      pPage.nCell--;
      data[pPage.hdrOffset + 3] = (byte)( pPage.nCell >> 8 ); data[pPage.hdrOffset + 4] = (byte)( pPage.nCell ); //put2byte( data, hdr + 3, pPage.nCell );
      pPage.nFree += 2;
    }

    /*
    ** Insert a new cell on pPage at cell index "i".  pCell points to the
    ** content of the cell.
    **
    ** If the cell content will fit on the page, then put it there.  If it
    ** will not fit, then make a copy of the cell content into pTemp if
    ** pTemp is not null.  Regardless of pTemp, allocate a new entry
    ** in pPage.aOvfl[] and make it point to the cell content (either
    ** in pTemp or the original pCell) and also record its index.
    ** Allocating a new entry in pPage.aCell[] implies that
    ** pPage.nOverflow is incremented.
    **
    ** If nSkip is non-zero, then do not copy the first nSkip bytes of the
    ** cell. The caller will overwrite them after this function returns. If
    ** nSkip is non-zero, then pCell may not point to an invalid memory location
    ** (but pCell+nSkip is always valid).
    */
    static void insertCell(
    MemPage pPage,      /* Page into which we are copying */
    int i,              /* New cell becomes the i-th cell of the page */
    u8[] pCell,         /* Content of the new cell */
    int sz,             /* Bytes of content in pCell */
    u8[] pTemp,         /* Temp storage space for pCell, if needed */
    Pgno iChild,        /* If non-zero, replace first 4 bytes with this value */
    ref int pRC         /* Read and write return code from here */
    )
    {
      int idx = 0;      /* Where to write new cell content in data[] */
      int j;            /* Loop counter */
      int end;          /* First byte past the last cell pointer in data[] */
      int ins;          /* Index in data[] where new cell pointer is inserted */
      int cellOffset;   /* Address of first cell pointer in data[] */
      u8[] data;        /* The content of the whole page */
      u8 ptr;           /* Used for moving information around in data[] */

      int nSkip = ( iChild != 0 ? 4 : 0 );

      if ( pRC != 0 ) return;

      Debug.Assert( i >= 0 && i <= pPage.nCell + pPage.nOverflow );
      Debug.Assert( pPage.nCell <= MX_CELL( pPage.pBt ) && MX_CELL( pPage.pBt ) <= 5460 );
      Debug.Assert( pPage.nOverflow <= ArraySize( pPage.aOvfl ) );
      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      /* The cell should normally be sized correctly.  However, when moving a
      ** malformed cell from a leaf page to an interior page, if the cell size
      ** wanted to be less than 4 but got rounded up to 4 on the leaf, then size
      ** might be less than 8 (leaf-size + pointer) on the interior node.  Hence
      ** the term after the || in the following assert(). */
      Debug.Assert( sz == cellSizePtr( pPage, pCell ) || ( sz == 8 && iChild > 0 ) );
      if ( pPage.nOverflow != 0 || sz + 2 > pPage.nFree )
      {
        if ( pTemp != null )
        {
          Buffer.BlockCopy( pCell, nSkip, pTemp, nSkip, sz - nSkip );//memcpy(pTemp+nSkip, pCell+nSkip, sz-nSkip);
          pCell = pTemp;
        }
        if ( iChild != 0 )
        {
          sqlite3Put4byte( pCell, iChild );
        }
        j = pPage.nOverflow++;
        Debug.Assert( j < pPage.aOvfl.Length );//(int)(sizeof(pPage.aOvfl)/sizeof(pPage.aOvfl[0])) );
        pPage.aOvfl[j].pCell = pCell;
        pPage.aOvfl[j].idx = (u16)i;
      }
      else
      {
        int rc = sqlite3PagerWrite( pPage.pDbPage );
        if ( rc != SQLITE_OK )
        {
          pRC = rc;
          return;
        }
        Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
        data = pPage.aData;
        cellOffset = pPage.cellOffset;
        end = cellOffset + 2 * pPage.nCell;
        ins = cellOffset + 2 * i;
        rc = allocateSpace( pPage, sz, ref idx );
        if ( rc != 0 ) { pRC = rc; return; }
        /* The allocateSpace() routine guarantees the following two properties
        ** if it returns success */
        Debug.Assert( idx >= end + 2 );
        Debug.Assert( idx + sz <= pPage.pBt.usableSize );
        pPage.nCell++;
        pPage.nFree -= (u16)( 2 + sz );
        Buffer.BlockCopy( pCell, nSkip, data, idx + nSkip, sz - nSkip ); //memcpy( data[idx + nSkip], pCell + nSkip, sz - nSkip );
        if ( iChild != 0 )
        {
          sqlite3Put4byte( data, idx, iChild );
        }
        //for(j=end, ptr=&data[j]; j>ins; j-=2, ptr-=2){
        //  ptr[0] = ptr[-2];
        //  ptr[1] = ptr[-1];
        //}
        for ( j = end; j > ins; j -= 2 )
        {
          data[j + 0] = data[j - 2];
          data[j + 1] = data[j - 1];
        }
        put2byte( data, ins, idx );
        put2byte( data, pPage.hdrOffset + 3, pPage.nCell );
#if !SQLITE_OMIT_AUTOVACUUM
        if ( pPage.pBt.autoVacuum )
        {
          /* The cell may contain a pointer to an overflow page. If so, write
          ** the entry for the overflow page into the pointer map.
          */
          ptrmapPutOvflPtr( pPage, pCell, ref pRC );
        }
#endif
      }
    }

    /*
    ** Add a list of cells to a page.  The page should be initially empty.
    ** The cells are guaranteed to fit on the page.
    */
    static void assemblePage(
    MemPage pPage,    /* The page to be assemblied */
    int nCell,        /* The number of cells to add to this page */
    u8[] apCell,      /* Pointer to a single the cell bodies */
    int[] aSize       /* Sizes of the cells bodie*/
    )
    {
      int i;            /* Loop counter */
      int pCellptr;     /* Address of next cell pointer */
      int cellbody;     /* Address of next cell body */
      byte[] data = pPage.aData;          /* Pointer to data for pPage */
      int hdr = pPage.hdrOffset;          /* Offset of header on pPage */
      int nUsable = pPage.pBt.usableSize; /* Usable size of page */

      Debug.Assert( pPage.nOverflow == 0 );
      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      Debug.Assert( nCell >= 0 && nCell <= MX_CELL( pPage.pBt ) && MX_CELL( pPage.pBt ) <= 5460 );
      Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );

      /* Check that the page has just been zeroed by zeroPage() */
      Debug.Assert( pPage.nCell == 0 );
      Debug.Assert( get2byte( data, hdr + 5 ) == nUsable );

      pCellptr = pPage.cellOffset + nCell * 2; //data[pPage.cellOffset + nCell * 2];
      cellbody = nUsable;
      for ( i = nCell - 1; i >= 0; i-- )
      {
        pCellptr -= 2;
        cellbody -= aSize[i];
        put2byte( data, pCellptr, cellbody );
        Buffer.BlockCopy( apCell, 0, data, cellbody, aSize[i] );//          memcpy(data[cellbody], apCell[i], aSize[i]);
      }
      put2byte( data, hdr + 3, nCell );
      put2byte( data, hdr + 5, cellbody );
      pPage.nFree -= (u16)( nCell * 2 + nUsable - cellbody );
      pPage.nCell = (u16)nCell;
    }
    static void assemblePage(
    MemPage pPage,    /* The page to be assemblied */
    int nCell,        /* The number of cells to add to this page */
    u8[][] apCell,    /* Pointers to cell bodies */
    u16[] aSize,      /* Sizes of the cells */
    int offset        /* Offset into the cell bodies, for c#  */
    )
    {
      int i;            /* Loop counter */
      int pCellptr;      /* Address of next cell pointer */
      int cellbody;     /* Address of next cell body */
      byte[] data = pPage.aData;          /* Pointer to data for pPage */
      int hdr = pPage.hdrOffset;          /* Offset of header on pPage */
      int nUsable = pPage.pBt.usableSize; /* Usable size of page */

      Debug.Assert( pPage.nOverflow == 0 );
      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      Debug.Assert( nCell >= 0 && nCell <= MX_CELL( pPage.pBt ) && MX_CELL( pPage.pBt ) <= 5460 );
      Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );

      /* Check that the page has just been zeroed by zeroPage() */
      Debug.Assert( pPage.nCell == 0 );
      Debug.Assert( get2byte( data, hdr + 5 ) == nUsable );

      pCellptr = pPage.cellOffset + nCell * 2; //data[pPage.cellOffset + nCell * 2];
      cellbody = nUsable;
      for ( i = nCell - 1; i >= 0; i-- )
      {
        pCellptr -= 2;
        cellbody -= aSize[i + offset];
        put2byte( data, pCellptr, cellbody );
        Buffer.BlockCopy( apCell[offset + i], 0, data, cellbody, aSize[i + offset] );//          memcpy(&data[cellbody], apCell[i], aSize[i]);
      }
      put2byte( data, hdr + 3, nCell );
      put2byte( data, hdr + 5, cellbody );
      pPage.nFree -= (u16)( nCell * 2 + nUsable - cellbody );
      pPage.nCell = (u16)nCell;
    }

    static void assemblePage(
    MemPage pPage,    /* The page to be assemblied */
    int nCell,        /* The number of cells to add to this page */
    u8[] apCell,      /* Pointers to cell bodies */
    u16[] aSize       /* Sizes of the cells */
    )
    {
      int i;            /* Loop counter */
      int pCellptr;     /* Address of next cell pointer */
      int cellbody;     /* Address of next cell body */
      u8[] data = pPage.aData;             /* Pointer to data for pPage */
      int hdr = pPage.hdrOffset;           /* Offset of header on pPage */
      int nUsable = pPage.pBt.usableSize; /* Usable size of page */

      Debug.Assert( pPage.nOverflow == 0 );
      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      Debug.Assert( nCell >= 0 && nCell <= MX_CELL( pPage.pBt ) && MX_CELL( pPage.pBt ) <= 5460 );
      Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );

      /* Check that the page has just been zeroed by zeroPage() */
      Debug.Assert( pPage.nCell == 0 );
      Debug.Assert( get2byte( data, hdr + 5 ) == nUsable );

      pCellptr = pPage.cellOffset + nCell * 2; //&data[pPage.cellOffset + nCell * 2];
      cellbody = nUsable;
      for ( i = nCell - 1; i >= 0; i-- )
      {
        pCellptr -= 2;
        cellbody -= aSize[i];
        put2byte( data, pCellptr, cellbody );
        Buffer.BlockCopy( apCell, 0, data, cellbody, aSize[i] );//memcpy( data[cellbody], apCell[i], aSize[i] );
      }
      put2byte( data, hdr + 3, nCell );
      put2byte( data, hdr + 5, cellbody );
      pPage.nFree -= (u16)( nCell * 2 + nUsable - cellbody );
      pPage.nCell = (u16)nCell;
    }

    /*
    ** The following parameters determine how many adjacent pages get involved
    ** in a balancing operation.  NN is the number of neighbors on either side
    ** of the page that participate in the balancing operation.  NB is the
    ** total number of pages that participate, including the target page and
    ** NN neighbors on either side.
    **
    ** The minimum value of NN is 1 (of course).  Increasing NN above 1
    ** (to 2 or 3) gives a modest improvement in SELECT and DELETE performance
    ** in exchange for a larger degradation in INSERT and UPDATE performance.
    ** The value of NN appears to give the best results overall.
    */
    static int NN = 1;              /* Number of neighbors on either side of pPage */
    static int NB = ( NN * 2 + 1 );   /* Total pages involved in the balance */

#if !SQLITE_OMIT_QUICKBALANCE
    /*
** This version of balance() handles the common special case where
** a new entry is being inserted on the extreme right-end of the
** tree, in other words, when the new entry will become the largest
** entry in the tree.
**
** Instead of trying to balance the 3 right-most leaf pages, just add
** a new page to the right-hand side and put the one new entry in
** that page.  This leaves the right side of the tree somewhat
** unbalanced.  But odds are that we will be inserting new entries
** at the end soon afterwards so the nearly empty page will quickly
** fill up.  On average.
**
** pPage is the leaf page which is the right-most page in the tree.
** pParent is its parent.  pPage must have a single overflow entry
** which is also the right-most entry on the page.
**
** The pSpace buffer is used to store a temporary copy of the divider
** cell that will be inserted into pParent. Such a cell consists of a 4
** byte page number followed by a variable length integer. In other
** words, at most 13 bytes. Hence the pSpace buffer must be at
** least 13 bytes in size.
*/
    static int balance_quick( MemPage pParent, MemPage pPage, u8[] pSpace )
    {
      BtShared pBt = pPage.pBt;    /* B-Tree Database */
      MemPage pNew = new MemPage();/* Newly allocated page */
      int rc;                      /* Return Code */
      Pgno pgnoNew = 0;              /* Page number of pNew */

      Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
      Debug.Assert( sqlite3PagerIswriteable( pParent.pDbPage ) );
      Debug.Assert( pPage.nOverflow == 1 );

      if ( pPage.nCell <= 0 )
        return SQLITE_CORRUPT_BKPT();

      /* Allocate a new page. This page will become the right-sibling of
** pPage. Make the parent page writable, so that the new divider cell
** may be inserted. If both these operations are successful, proceed.
*/
      rc = allocateBtreePage( pBt, ref pNew, ref pgnoNew, 0, 0 );

      if ( rc == SQLITE_OK )
      {

        int pOut = 4;//u8 pOut = &pSpace[4];
        u8[] pCell = pPage.aOvfl[0].pCell;
        int[] szCell = new int[1]; szCell[0] = cellSizePtr( pPage, pCell );
        int pStop;

        Debug.Assert( sqlite3PagerIswriteable( pNew.pDbPage ) );
        Debug.Assert( pPage.aData[0] == ( PTF_INTKEY | PTF_LEAFDATA | PTF_LEAF ) );
        zeroPage( pNew, PTF_INTKEY | PTF_LEAFDATA | PTF_LEAF );
        assemblePage( pNew, 1, pCell, szCell );

        /* If this is an auto-vacuum database, update the pointer map
        ** with entries for the new page, and any pointer from the
        ** cell on the page to an overflow page. If either of these
        ** operations fails, the return code is set, but the contents
        ** of the parent page are still manipulated by thh code below.
        ** That is Ok, at this point the parent page is guaranteed to
        ** be marked as dirty. Returning an error code will cause a
        ** rollback, undoing any changes made to the parent page.
        */
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
        if ( pBt.autoVacuum )
#else
if (false)
#endif
        {
          ptrmapPut( pBt, pgnoNew, PTRMAP_BTREE, pParent.pgno, ref rc );
          if ( szCell[0] > pNew.minLocal )
          {
            ptrmapPutOvflPtr( pNew, pCell, ref rc );
          }
        }

        /* Create a divider cell to insert into pParent. The divider cell
        ** consists of a 4-byte page number (the page number of pPage) and
        ** a variable length key value (which must be the same value as the
        ** largest key on pPage).
        **
        ** To find the largest key value on pPage, first find the right-most
        ** cell on pPage. The first two fields of this cell are the
        ** record-length (a variable length integer at most 32-bits in size)
        ** and the key value (a variable length integer, may have any value).
        ** The first of the while(...) loops below skips over the record-length
        ** field. The second while(...) loop copies the key value from the
        ** cell on pPage into the pSpace buffer.
        */
        int iCell = findCell( pPage, pPage.nCell - 1 ); //pCell = findCell( pPage, pPage.nCell - 1 );
        pCell = pPage.aData;
        int _pCell = iCell;
        pStop = _pCell + 9; //pStop = &pCell[9];
        while ( ( ( pCell[_pCell++] ) & 0x80 ) != 0 && _pCell < pStop ) ; //while ( ( *( pCell++ ) & 0x80 ) && pCell < pStop ) ;
        pStop = _pCell + 9;//pStop = &pCell[9];
        while ( ( ( pSpace[pOut++] = pCell[_pCell++] ) & 0x80 ) != 0 && _pCell < pStop ) ; //while ( ( ( *( pOut++ ) = *( pCell++ ) ) & 0x80 ) && pCell < pStop ) ;

        /* Insert the new divider cell into pParent. */
        insertCell( pParent, pParent.nCell, pSpace, pOut, //(int)(pOut-pSpace),
        null, pPage.pgno, ref rc );

        /* Set the right-child pointer of pParent to point to the new page. */
        sqlite3Put4byte( pParent.aData, pParent.hdrOffset + 8, pgnoNew );

        /* Release the reference to the new page. */
        releasePage( pNew );
      }

      return rc;
    }
#endif //* SQLITE_OMIT_QUICKBALANCE */

#if FALSE
/*
** This function does not contribute anything to the operation of SQLite.
** it is sometimes activated temporarily while debugging code responsible
** for setting pointer-map entries.
*/
static int ptrmapCheckPages(MemPage **apPage, int nPage){
int i, j;
for(i=0; i<nPage; i++){
Pgno n;
u8 e;
MemPage pPage = apPage[i];
BtShared pBt = pPage.pBt;
Debug.Assert( pPage.isInit!=0 );

for(j=0; j<pPage.nCell; j++){
CellInfo info;
u8 *z;

z = findCell(pPage, j);
btreeParseCellPtr(pPage, z,  info);
if( info.iOverflow ){
Pgno ovfl = sqlite3Get4byte(z[info.iOverflow]);
ptrmapGet(pBt, ovfl, ref e, ref n);
Debug.Assert( n==pPage.pgno && e==PTRMAP_OVERFLOW1 );
}
if( 0==pPage.leaf ){
Pgno child = sqlite3Get4byte(z);
ptrmapGet(pBt, child, ref e, ref n);
Debug.Assert( n==pPage.pgno && e==PTRMAP_BTREE );
}
}
if( 0==pPage.leaf ){
Pgno child = sqlite3Get4byte(pPage.aData,pPage.hdrOffset+8]);
ptrmapGet(pBt, child, ref e, ref n);
Debug.Assert( n==pPage.pgno && e==PTRMAP_BTREE );
}
}
return 1;
}
#endif

    /*
** This function is used to copy the contents of the b-tree node stored
** on page pFrom to page pTo. If page pFrom was not a leaf page, then
** the pointer-map entries for each child page are updated so that the
** parent page stored in the pointer map is page pTo. If pFrom contained
** any cells with overflow page pointers, then the corresponding pointer
** map entries are also updated so that the parent page is page pTo.
**
** If pFrom is currently carrying any overflow cells (entries in the
** MemPage.aOvfl[] array), they are not copied to pTo.
**
** Before returning, page pTo is reinitialized using btreeInitPage().
**
** The performance of this function is not critical. It is only used by
** the balance_shallower() and balance_deeper() procedures, neither of
** which are called often under normal circumstances.
*/
    static void copyNodeContent( MemPage pFrom, MemPage pTo, ref int pRC )
    {
      if ( ( pRC ) == SQLITE_OK )
      {
        BtShared pBt = pFrom.pBt;
        u8[] aFrom = pFrom.aData;
        u8[] aTo = pTo.aData;
        int iFromHdr = pFrom.hdrOffset;
        int iToHdr = ( ( pTo.pgno == 1 ) ? 100 : 0 );
        int rc;
        int iData;


        Debug.Assert( pFrom.isInit != 0 );
        Debug.Assert( pFrom.nFree >= iToHdr );
        Debug.Assert( get2byte( aFrom, iFromHdr + 5 ) <= pBt.usableSize );

        /* Copy the b-tree node content from page pFrom to page pTo. */
        iData = get2byte( aFrom, iFromHdr + 5 );
        Buffer.BlockCopy( aFrom, iData, aTo, iData, pBt.usableSize - iData );//memcpy(aTo[iData], ref aFrom[iData], pBt.usableSize-iData);
        Buffer.BlockCopy( aFrom, iFromHdr, aTo, iToHdr, pFrom.cellOffset + 2 * pFrom.nCell );//memcpy(aTo[iToHdr], ref aFrom[iFromHdr], pFrom.cellOffset + 2*pFrom.nCell);

        /* Reinitialize page pTo so that the contents of the MemPage structure
        ** match the new data. The initialization of pTo can actually fail under
        ** fairly obscure circumstances, even though it is a copy of initialized 
        ** page pFrom.
        */
        pTo.isInit = 0;
        rc = btreeInitPage( pTo );
        if ( rc != SQLITE_OK )
        {
          pRC = rc;
          return;
        }

        /* If this is an auto-vacuum database, update the pointer-map entries
        ** for any b-tree or overflow pages that pTo now contains the pointers to.
        */
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
        if ( pBt.autoVacuum )
#else
if (false)
#endif
        {
          pRC = setChildPtrmaps( pTo );
        }
      }
    }

    /*
    ** This routine redistributes cells on the iParentIdx'th child of pParent
    ** (hereafter "the page") and up to 2 siblings so that all pages have about the
    ** same amount of free space. Usually a single sibling on either side of the
    ** page are used in the balancing, though both siblings might come from one
    ** side if the page is the first or last child of its parent. If the page
    ** has fewer than 2 siblings (something which can only happen if the page
    ** is a root page or a child of a root page) then all available siblings
    ** participate in the balancing.
    **
    ** The number of siblings of the page might be increased or decreased by
    ** one or two in an effort to keep pages nearly full but not over full.
    **
    ** Note that when this routine is called, some of the cells on the page
    ** might not actually be stored in MemPage.aData[]. This can happen
    ** if the page is overfull. This routine ensures that all cells allocated
    ** to the page and its siblings fit into MemPage.aData[] before returning.
    **
    ** In the course of balancing the page and its siblings, cells may be
    ** inserted into or removed from the parent page (pParent). Doing so
    ** may cause the parent page to become overfull or underfull. If this
    ** happens, it is the responsibility of the caller to invoke the correct
    ** balancing routine to fix this problem (see the balance() routine).
    **
    ** If this routine fails for any reason, it might leave the database
    ** in a corrupted state. So if this routine fails, the database should
    ** be rolled back.
    **
    ** The third argument to this function, aOvflSpace, is a pointer to a
    ** buffer big enough to hold one page. If while inserting cells into the parent
    ** page (pParent) the parent page becomes overfull, this buffer is
    ** used to store the parent's overflow cells. Because this function inserts
    ** a maximum of four divider cells into the parent page, and the maximum
    ** size of a cell stored within an internal node is always less than 1/4
    ** of the page-size, the aOvflSpace[] buffer is guaranteed to be large
    ** enough for all overflow cells.
    **
    ** If aOvflSpace is set to a null pointer, this function returns
    ** SQLITE_NOMEM.
    */

    // under C#; Try to reuse Memory

    static int balance_nonroot(
    MemPage pParent,               /* Parent page of siblings being balanced */
    int iParentIdx,                /* Index of "the page" in pParent */
    u8[] aOvflSpace,               /* page-size bytes of space for parent ovfl */
    int isRoot                     /* True if pParent is a root-page */
    )
    {
     MemPage[] apOld = new MemPage[NB];    /* pPage and up to two siblings */
     MemPage[] apCopy = new MemPage[NB];   /* Private copies of apOld[] pages */
     MemPage[] apNew = new MemPage[NB + 2];/* pPage and up to NB siblings after balancing */
     int[] apDiv = new int[NB - 1];        /* Divider cells in pParent */
     int[] cntNew = new int[NB + 2];       /* Index in aCell[] of cell after i-th page */
     int[] szNew = new int[NB + 2];        /* Combined size of cells place on i-th page */
     u16[] szCell = new u16[1];            /* Local size of all cells in apCell[] */
      BtShared pBt;                /* The whole database */
      int nCell = 0;               /* Number of cells in apCell[] */
      int nMaxCells = 0;           /* Allocated size of apCell, szCell, aFrom. */
      int nNew = 0;                /* Number of pages in apNew[] */
      int nOld;                    /* Number of pages in apOld[] */
      int i, j, k;                 /* Loop counters */
      int nxDiv;                   /* Next divider slot in pParent.aCell[] */
      int rc = SQLITE_OK;          /* The return code */
      u16 leafCorrection;          /* 4 if pPage is a leaf.  0 if not */
      int leafData;                /* True if pPage is a leaf of a LEAFDATA tree */
      int usableSpace;             /* Bytes in pPage beyond the header */
      int pageFlags;               /* Value of pPage.aData[0] */
      int subtotal;                /* Subtotal of bytes in cells on one page */
      //int iSpace1 = 0;             /* First unused byte of aSpace1[] */
      int iOvflSpace = 0;          /* First unused byte of aOvflSpace[] */
      int szScratch;               /* Size of scratch memory requested */
      //MemPage[] apOld = new MemPage[NB];    /* pPage and up to two siblings */
      //MemPage[] apCopy = new MemPage[NB];   /* Private copies of apOld[] pages */
      //MemPage[] apNew = new MemPage[NB + 2];/* pPage and up to NB siblings after balancing */
      int pRight;                  /* Location in parent of right-sibling pointer */
      //int[] apDiv = new int[NB - 1];        /* Divider cells in pParent */
      //int[] cntNew = new int[NB + 2];       /* Index in aCell[] of cell after i-th page */
      //int[] szNew = new int[NB + 2];        /* Combined size of cells place on i-th page */
      u8[][] apCell = null;                 /* All cells begin balanced */
      //u16[] szCell;                         /* Local size of all cells in apCell[] */
      //u8[] aSpace1;                         /* Space for copies of dividers cells */
      Pgno pgno;                   /* Temp var to store a page number in */

      pBt = pParent.pBt;
      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      Debug.Assert( sqlite3PagerIswriteable( pParent.pDbPage ) );

#if FALSE
TRACE("BALANCE: begin page %d child of %d\n", pPage.pgno, pParent.pgno);
#endif

      /* At this point pParent may have at most one overflow cell. And if
** this overflow cell is present, it must be the cell with
** index iParentIdx. This scenario comes about when this function
** is called (indirectly) from sqlite3BtreeDelete().
*/
      Debug.Assert( pParent.nOverflow == 0 || pParent.nOverflow == 1 );
      Debug.Assert( pParent.nOverflow == 0 || pParent.aOvfl[0].idx == iParentIdx );

      //if( !aOvflSpace ){
      //  return SQLITE_NOMEM;
      //}

      /* Find the sibling pages to balance. Also locate the cells in pParent
      ** that divide the siblings. An attempt is made to find NN siblings on
      ** either side of pPage. More siblings are taken from one side, however,
      ** if there are fewer than NN siblings on the other side. If pParent
      ** has NB or fewer children then all children of pParent are taken.
      **
      ** This loop also drops the divider cells from the parent page. This
      ** way, the remainder of the function does not have to deal with any
      ** overflow cells in the parent page, since if any existed they will
      ** have already been removed.
      */
      i = pParent.nOverflow + pParent.nCell;
      if ( i < 2 )
      {
        nxDiv = 0;
        nOld = i + 1;
      }
      else
      {
        nOld = 3;
        if ( iParentIdx == 0 )
        {
          nxDiv = 0;
        }
        else if ( iParentIdx == i )
        {
          nxDiv = i - 2;
        }
        else
        {
          nxDiv = iParentIdx - 1;
        }
        i = 2;
      }
      if ( ( i + nxDiv - pParent.nOverflow ) == pParent.nCell )
      {
        pRight = pParent.hdrOffset + 8; //&pParent.aData[pParent.hdrOffset + 8];
      }
      else
      {
        pRight = findCell( pParent, i + nxDiv - pParent.nOverflow );
      }
      pgno = sqlite3Get4byte( pParent.aData, pRight );
      while ( true )
      {
        rc = getAndInitPage( pBt, pgno, ref apOld[i] );
        if ( rc != 0 )
        {
          apOld = new MemPage[i + 1];//memset(apOld, 0, (i+1)*sizeof(MemPage*));
          goto balance_cleanup;
        }
        nMaxCells += 1 + apOld[i].nCell + apOld[i].nOverflow;
        if ( ( i-- ) == 0 ) break;

        if ( i + nxDiv == pParent.aOvfl[0].idx && pParent.nOverflow != 0 )
        {
          apDiv[i] = 0;// = pParent.aOvfl[0].pCell;
          pgno = sqlite3Get4byte( pParent.aOvfl[0].pCell, apDiv[i] );
          szNew[i] = cellSizePtr( pParent, apDiv[i] );
          pParent.nOverflow = 0;
        }
        else
        {
          apDiv[i] = findCell( pParent, i + nxDiv - pParent.nOverflow );
          pgno = sqlite3Get4byte( pParent.aData, apDiv[i] );
          szNew[i] = cellSizePtr( pParent, apDiv[i] );

          /* Drop the cell from the parent page. apDiv[i] still points to
          ** the cell within the parent, even though it has been dropped.
          ** This is safe because dropping a cell only overwrites the first
          ** four bytes of it, and this function does not need the first
          ** four bytes of the divider cell. So the pointer is safe to use
          ** later on.
          **
          ** Unless SQLite is compiled in secure-delete mode. In this case,
          ** the dropCell() routine will overwrite the entire cell with zeroes.
          ** In this case, temporarily copy the cell into the aOvflSpace[]
          ** buffer. It will be copied out again as soon as the aSpace[] buffer
          ** is allocated.  */
          //if (pBt.secureDelete)
          //{
          //  int iOff = (int)(apDiv[i]) - (int)(pParent.aData); //SQLITE_PTR_TO_INT(apDiv[i]) - SQLITE_PTR_TO_INT(pParent.aData);
          //  if ((iOff + szNew[i]) > pBt.usableSize)
          //  {
          //    rc = SQLITE_CORRUPT_BKPT();
          //    Array.Clear(apOld[0].aData,0,apOld[0].aData.Length); //memset(apOld, 0, (i + 1) * sizeof(MemPage*));
          //    goto balance_cleanup;
          //  }
          //  else
          //  {
          //    memcpy(&aOvflSpace[iOff], apDiv[i], szNew[i]);
          //    apDiv[i] = &aOvflSpace[apDiv[i] - pParent.aData];
          //  }
          //}
          dropCell(pParent, i + nxDiv - pParent.nOverflow, szNew[i], ref rc);
        }
      }

      /* Make nMaxCells a multiple of 4 in order to preserve 8-byte
      ** alignment */
      nMaxCells = ( nMaxCells + 3 ) & ~3;

      /*
      ** Allocate space for memory structures
      */
      //k = pBt.pageSize + ROUND8(sizeof(MemPage));
      //szScratch =
      //     nMaxCells*sizeof(u8*)                       /* apCell */
      //   + nMaxCells*sizeof(u16)                       /* szCell */
      //   + pBt.pageSize                               /* aSpace1 */
      //   + k*nOld;                                     /* Page copies (apCopy) */
      apCell = sqlite3ScratchMalloc(apCell, nMaxCells); 
      //if( apCell==null ){
      //  rc = SQLITE_NOMEM;
      //  goto balance_cleanup;
      //}
      if (szCell.Length < nMaxCells) Array.Resize(ref szCell, nMaxCells); //(u16*)&apCell[nMaxCells];
      //aSpace1 = new byte[pBt.pageSize * (nMaxCells)];//  aSpace1 = (u8*)&szCell[nMaxCells];
      //Debug.Assert( EIGHT_BYTE_ALIGNMENT(aSpace1) );

      /*
      ** Load pointers to all cells on sibling pages and the divider cells
      ** into the local apCell[] array.  Make copies of the divider cells
      ** into space obtained from aSpace1[] and remove the the divider Cells
      ** from pParent.
      **
      ** If the siblings are on leaf pages, then the child pointers of the
      ** divider cells are stripped from the cells before they are copied
      ** into aSpace1[].  In this way, all cells in apCell[] are without
      ** child pointers.  If siblings are not leaves, then all cell in
      ** apCell[] include child pointers.  Either way, all cells in apCell[]
      ** are alike.
      **
      ** leafCorrection:  4 if pPage is a leaf.  0 if pPage is not a leaf.
      **       leafData:  1 if pPage holds key+data and pParent holds only keys.
      */
      leafCorrection = (u16)( apOld[0].leaf * 4 );
      leafData = apOld[0].hasData;
      for ( i = 0; i < nOld; i++ )
      {
        int limit;

        /* Before doing anything else, take a copy of the i'th original sibling
        ** The rest of this function will use data from the copies rather
        ** that the original pages since the original pages will be in the
        ** process of being overwritten.  */
        //MemPage pOld = apCopy[i] = (MemPage*)&aSpace1[pBt.pageSize + k*i];
        //memcpy(pOld, apOld[i], sizeof(MemPage));
        //pOld.aData = (void*)&pOld[1];
        //memcpy(pOld.aData, apOld[i].aData, pBt.pageSize);
        MemPage pOld = apCopy[i] = apOld[i].Copy();

        limit = pOld.nCell + pOld.nOverflow;
        for ( j = 0; j < limit; j++ )
        {
          Debug.Assert( nCell < nMaxCells );
          //apCell[nCell] = findOverflowCell( pOld, j );
          //szCell[nCell] = cellSizePtr( pOld, apCell, nCell );
          int iFOFC = findOverflowCell( pOld, j );
          szCell[nCell] = cellSizePtr( pOld, iFOFC );
          // Copy the Data Locally
          if (apCell[nCell] == null) apCell[nCell] = new u8[szCell[nCell]];
            else if (apCell[nCell].Length < szCell[nCell]) Array.Resize(ref apCell[nCell] ,szCell[nCell]);
          if ( iFOFC < 0 )  // Overflow Cell
            Buffer.BlockCopy( pOld.aOvfl[-( iFOFC + 1 )].pCell, 0, apCell[nCell], 0, szCell[nCell] );
          else
            Buffer.BlockCopy( pOld.aData, iFOFC, apCell[nCell], 0, szCell[nCell] );
          nCell++;
        }
        if ( i < nOld - 1 && 0 == leafData )
        {
          u16 sz = (u16)szNew[i];
          byte[] pTemp = sqlite3Malloc(sz + leafCorrection);
          Debug.Assert( nCell < nMaxCells );
          szCell[nCell] = sz;
          //pTemp = &aSpace1[iSpace1];
          //iSpace1 += sz;
          Debug.Assert( sz <= pBt.pageSize / 4 );
          //Debug.Assert(iSpace1 <= pBt.pageSize);
          Buffer.BlockCopy( pParent.aData, apDiv[i], pTemp, 0, sz );//memcpy( pTemp, apDiv[i], sz );
          if (apCell[nCell] == null || apCell[nCell].Length < sz) Array.Resize(ref apCell[nCell] ,sz);
          Buffer.BlockCopy( pTemp, leafCorrection, apCell[nCell], 0, sz );//apCell[nCell] = pTemp + leafCorrection;
          Debug.Assert( leafCorrection == 0 || leafCorrection == 4 );
          szCell[nCell] = (u16)( szCell[nCell] - leafCorrection );
          if ( 0 == pOld.leaf )
          {
            Debug.Assert( leafCorrection == 0 );
            Debug.Assert( pOld.hdrOffset == 0 );
            /* The right pointer of the child page pOld becomes the left
            ** pointer of the divider cell */
            Buffer.BlockCopy( pOld.aData, 8, apCell[nCell], 0, 4 );//memcpy( apCell[nCell], ref pOld.aData[8], 4 );
          }
          else
          {
            Debug.Assert( leafCorrection == 4 );
            if ( szCell[nCell] < 4 )
            {
              /* Do not allow any cells smaller than 4 bytes. */
              szCell[nCell] = 4;
            }
          }
          nCell++;
        }
      }

      /*
      ** Figure out the number of pages needed to hold all nCell cells.
      ** Store this number in "k".  Also compute szNew[] which is the total
      ** size of all cells on the i-th page and cntNew[] which is the index
      ** in apCell[] of the cell that divides page i from page i+1.
      ** cntNew[k] should equal nCell.
      **
      ** Values computed by this block:
      **
      **           k: The total number of sibling pages
      **    szNew[i]: Spaced used on the i-th sibling page.
      **   cntNew[i]: Index in apCell[] and szCell[] for the first cell to
      **              the right of the i-th sibling page.
      ** usableSpace: Number of bytes of space available on each sibling.
      **
      */
      usableSpace = pBt.usableSize - 12 + leafCorrection;
      for ( subtotal = k = i = 0; i < nCell; i++ )
      {
        Debug.Assert( i < nMaxCells );
        subtotal += szCell[i] + 2;
        if ( subtotal > usableSpace )
        {
          szNew[k] = subtotal - szCell[i];
          cntNew[k] = i;
          if ( leafData != 0 ) { i--; }
          subtotal = 0;
          k++;
          if ( k > NB + 1 ) { rc = SQLITE_CORRUPT_BKPT(); goto balance_cleanup; }
        }
      }
      szNew[k] = subtotal;
      cntNew[k] = nCell;
      k++;

      /*
      ** The packing computed by the previous block is biased toward the siblings
      ** on the left side.  The left siblings are always nearly full, while the
      ** right-most sibling might be nearly empty.  This block of code attempts
      ** to adjust the packing of siblings to get a better balance.
      **
      ** This adjustment is more than an optimization.  The packing above might
      ** be so out of balance as to be illegal.  For example, the right-most
      ** sibling might be completely empty.  This adjustment is not optional.
      */
      for ( i = k - 1; i > 0; i-- )
      {
        int szRight = szNew[i];  /* Size of sibling on the right */
        int szLeft = szNew[i - 1]; /* Size of sibling on the left */
        int r;              /* Index of right-most cell in left sibling */
        int d;              /* Index of first cell to the left of right sibling */

        r = cntNew[i - 1] - 1;
        d = r + 1 - leafData;
        Debug.Assert( d < nMaxCells );
        Debug.Assert( r < nMaxCells );
        while ( szRight == 0 || szRight + szCell[d] + 2 <= szLeft - ( szCell[r] + 2 ) )
        {
          szRight += szCell[d] + 2;
          szLeft -= szCell[r] + 2;
          cntNew[i - 1]--;
          r = cntNew[i - 1] - 1;
          d = r + 1 - leafData;
        }
        szNew[i] = szRight;
        szNew[i - 1] = szLeft;
      }

      /* Either we found one or more cells (cntnew[0])>0) or pPage is
      ** a virtual root page.  A virtual root page is when the real root
      ** page is page 1 and we are the only child of that page.
      */
      Debug.Assert( cntNew[0] > 0 || ( pParent.pgno == 1 && pParent.nCell == 0 ) );

      TRACE( "BALANCE: old: %d %d %d  ",
      apOld[0].pgno,
      nOld >= 2 ? apOld[1].pgno : 0,
      nOld >= 3 ? apOld[2].pgno : 0
      );

      /*
      ** Allocate k new pages.  Reuse old pages where possible.
      */
      if ( apOld[0].pgno <= 1 )
      {
        rc = SQLITE_CORRUPT_BKPT();
        goto balance_cleanup;
      }
      pageFlags = apOld[0].aData[0];
      for ( i = 0; i < k; i++ )
      {
        MemPage pNew = new MemPage();
        if ( i < nOld )
        {
          pNew = apNew[i] = apOld[i];
          apOld[i] = null;
          rc = sqlite3PagerWrite( pNew.pDbPage );
          nNew++;
          if ( rc != 0 ) goto balance_cleanup;
        }
        else
        {
          Debug.Assert( i > 0 );
          rc = allocateBtreePage( pBt, ref pNew, ref pgno, pgno, 0 );
          if ( rc != 0 ) goto balance_cleanup;
          apNew[i] = pNew;
          nNew++;

          /* Set the pointer-map entry for the new sibling page. */
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
          if ( pBt.autoVacuum )
#else
if (false)
#endif
          {
            ptrmapPut( pBt, pNew.pgno, PTRMAP_BTREE, pParent.pgno, ref rc );
            if ( rc != SQLITE_OK )
            {
              goto balance_cleanup;
            }
          }
        }
      }

      /* Free any old pages that were not reused as new pages.
      */
      while ( i < nOld )
      {
        freePage( apOld[i], ref rc );
        if ( rc != 0 ) goto balance_cleanup;
        releasePage( apOld[i] );
        apOld[i] = null;
        i++;
      }

      /*
      ** Put the new pages in accending order.  This helps to
      ** keep entries in the disk file in order so that a scan
      ** of the table is a linear scan through the file.  That
      ** in turn helps the operating system to deliver pages
      ** from the disk more rapidly.
      **
      ** An O(n^2) insertion sort algorithm is used, but since
      ** n is never more than NB (a small constant), that should
      ** not be a problem.
      **
      ** When NB==3, this one optimization makes the database
      ** about 25% faster for large insertions and deletions.
      */
      for ( i = 0; i < k - 1; i++ )
      {
        int minV = (int)apNew[i].pgno;
        int minI = i;
        for ( j = i + 1; j < k; j++ )
        {
          if ( apNew[j].pgno < (u32)minV )
          {
            minI = j;
            minV = (int)apNew[j].pgno;
          }
        }
        if ( minI > i )
        {
          int t;
          MemPage pT;
          t = (int)apNew[i].pgno;
          pT = apNew[i];
          apNew[i] = apNew[minI];
          apNew[minI] = pT;
        }
      }
      TRACE( "new: %d(%d) %d(%d) %d(%d) %d(%d) %d(%d)\n",
      apNew[0].pgno, szNew[0],
      nNew >= 2 ? apNew[1].pgno : 0, nNew >= 2 ? szNew[1] : 0,
      nNew >= 3 ? apNew[2].pgno : 0, nNew >= 3 ? szNew[2] : 0,
      nNew >= 4 ? apNew[3].pgno : 0, nNew >= 4 ? szNew[3] : 0,
      nNew >= 5 ? apNew[4].pgno : 0, nNew >= 5 ? szNew[4] : 0 );

      Debug.Assert( sqlite3PagerIswriteable( pParent.pDbPage ) );
      sqlite3Put4byte( pParent.aData, pRight, apNew[nNew - 1].pgno );

      /*
      ** Evenly distribute the data in apCell[] across the new pages.
      ** Insert divider cells into pParent as necessary.
      */
      j = 0;
      for ( i = 0; i < nNew; i++ )
      {
        /* Assemble the new sibling page. */
        MemPage pNew = apNew[i];
        Debug.Assert( j < nMaxCells );
        zeroPage( pNew, pageFlags );
        assemblePage( pNew, cntNew[i] - j, apCell, szCell, j );
        Debug.Assert( pNew.nCell > 0 || ( nNew == 1 && cntNew[0] == 0 ) );
        Debug.Assert( pNew.nOverflow == 0 );

        j = cntNew[i];

        /* If the sibling page assembled above was not the right-most sibling,
        ** insert a divider cell into the parent page.
        */
        Debug.Assert( i < nNew - 1 || j == nCell );
        if ( j < nCell )
        {
          u8[] pCell;
          u8[] pTemp;
          int sz;

          Debug.Assert( j < nMaxCells );
          pCell = apCell[j];
          sz = szCell[j] + leafCorrection;
          pTemp = sqlite3Malloc(sz);//&aOvflSpace[iOvflSpace];
          if ( 0 == pNew.leaf )
          {
            Buffer.BlockCopy( pCell, 0, pNew.aData, 8, 4 );//memcpy( pNew.aData[8], pCell, 4 );
          }
          else if ( leafData != 0 )
          {
            /* If the tree is a leaf-data tree, and the siblings are leaves,
            ** then there is no divider cell in apCell[]. Instead, the divider
            ** cell consists of the integer key for the right-most cell of
            ** the sibling-page assembled above only.
            */
            CellInfo info = new CellInfo();
            j--;
            btreeParseCellPtr( pNew, apCell[j], ref info );
            pCell = pTemp;
            sz = 4 + putVarint( pCell, 4, (u64)info.nKey );
            pTemp = null;
          }
          else
          {
            //------------ pCell -= 4;
            byte[] _pCell_4 = sqlite3Malloc(pCell.Length + 4);
            Buffer.BlockCopy( pCell, 0, _pCell_4, 4, pCell.Length );
            pCell = _pCell_4;
            //
            /* Obscure case for non-leaf-data trees: If the cell at pCell was
            ** previously stored on a leaf node, and its reported size was 4
            ** bytes, then it may actually be smaller than this
            ** (see btreeParseCellPtr(), 4 bytes is the minimum size of
            ** any cell). But it is important to pass the correct size to
            ** insertCell(), so reparse the cell now.
            **
            ** Note that this can never happen in an SQLite data file, as all
            ** cells are at least 4 bytes. It only happens in b-trees used
            ** to evaluate "IN (SELECT ...)" and similar clauses.
            */
            if ( szCell[j] == 4 )
            {
              Debug.Assert( leafCorrection == 4 );
              sz = cellSizePtr( pParent, pCell );
            }
          }
          iOvflSpace += sz;
          Debug.Assert( sz <= pBt.pageSize / 4 );
          Debug.Assert( iOvflSpace <= pBt.pageSize );
          insertCell( pParent, nxDiv, pCell, sz, pTemp, pNew.pgno, ref rc );
          if ( rc != SQLITE_OK ) goto balance_cleanup;
          Debug.Assert( sqlite3PagerIswriteable( pParent.pDbPage ) );

          j++;
          nxDiv++;
        }
      }
      Debug.Assert( j == nCell );
      Debug.Assert( nOld > 0 );
      Debug.Assert( nNew > 0 );
      if ( ( pageFlags & PTF_LEAF ) == 0 )
      {
        Buffer.BlockCopy( apCopy[nOld - 1].aData, 8, apNew[nNew - 1].aData, 8, 4 ); //u8* zChild = &apCopy[nOld - 1].aData[8];
        //memcpy( apNew[nNew - 1].aData[8], zChild, 4 );
      }

      if ( isRoot != 0 && pParent.nCell == 0 && pParent.hdrOffset <= apNew[0].nFree )
      {
        /* The root page of the b-tree now contains no cells. The only sibling
        ** page is the right-child of the parent. Copy the contents of the
        ** child page into the parent, decreasing the overall height of the
        ** b-tree structure by one. This is described as the "balance-shallower"
        ** sub-algorithm in some documentation.
        **
        ** If this is an auto-vacuum database, the call to copyNodeContent()
        ** sets all pointer-map entries corresponding to database image pages
        ** for which the pointer is stored within the content being copied.
        **
        ** The second Debug.Assert below verifies that the child page is defragmented
        ** (it must be, as it was just reconstructed using assemblePage()). This
        ** is important if the parent page happens to be page 1 of the database
        ** image.  */
        Debug.Assert( nNew == 1 );
        Debug.Assert( apNew[0].nFree ==
        ( get2byte( apNew[0].aData, 5 ) - apNew[0].cellOffset - apNew[0].nCell * 2 )
        );
        copyNodeContent( apNew[0], pParent, ref rc );
        freePage( apNew[0], ref rc );
      }
      else
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
        if ( pBt.autoVacuum )
#else
if (false)
#endif
        {
          /* Fix the pointer-map entries for all the cells that were shifted around.
          ** There are several different types of pointer-map entries that need to
          ** be dealt with by this routine. Some of these have been set already, but
          ** many have not. The following is a summary:
          **
          **   1) The entries associated with new sibling pages that were not
          **      siblings when this function was called. These have already
          **      been set. We don't need to worry about old siblings that were
          **      moved to the free-list - the freePage() code has taken care
          **      of those.
          **
          **   2) The pointer-map entries associated with the first overflow
          **      page in any overflow chains used by new divider cells. These
          **      have also already been taken care of by the insertCell() code.
          **
          **   3) If the sibling pages are not leaves, then the child pages of
          **      cells stored on the sibling pages may need to be updated.
          **
          **   4) If the sibling pages are not internal intkey nodes, then any
          **      overflow pages used by these cells may need to be updated
          **      (internal intkey nodes never contain pointers to overflow pages).
          **
          **   5) If the sibling pages are not leaves, then the pointer-map
          **      entries for the right-child pages of each sibling may need
          **      to be updated.
          **
          ** Cases 1 and 2 are dealt with above by other code. The next
          ** block deals with cases 3 and 4 and the one after that, case 5. Since
          ** setting a pointer map entry is a relatively expensive operation, this
          ** code only sets pointer map entries for child or overflow pages that have
          ** actually moved between pages.  */
          MemPage pNew = apNew[0];
          MemPage pOld = apCopy[0];
          int nOverflow = pOld.nOverflow;
          int iNextOld = pOld.nCell + nOverflow;
          int iOverflow = ( nOverflow != 0 ? pOld.aOvfl[0].idx : -1 );
          j = 0;                             /* Current 'old' sibling page */
          k = 0;                             /* Current 'new' sibling page */
          for ( i = 0; i < nCell; i++ )
          {
            int isDivider = 0;
            while ( i == iNextOld )
            {
              /* Cell i is the cell immediately following the last cell on old
              ** sibling page j. If the siblings are not leaf pages of an
              ** intkey b-tree, then cell i was a divider cell. */
              pOld = apCopy[++j];
              iNextOld = i + ( 0 == leafData ? 1 : 0 ) + pOld.nCell + pOld.nOverflow;
              if ( pOld.nOverflow != 0 )
              {
                nOverflow = pOld.nOverflow;
                iOverflow = i + ( 0 == leafData ? 1 : 0 ) + pOld.aOvfl[0].idx;
              }
              isDivider = 0 == leafData ? 1 : 0;
            }

            Debug.Assert( nOverflow > 0 || iOverflow < i );
            Debug.Assert( nOverflow < 2 || pOld.aOvfl[0].idx == pOld.aOvfl[1].idx - 1 );
            Debug.Assert( nOverflow < 3 || pOld.aOvfl[1].idx == pOld.aOvfl[2].idx - 1 );
            if ( i == iOverflow )
            {
              isDivider = 1;
              if ( ( --nOverflow ) > 0 )
              {
                iOverflow++;
              }
            }

            if ( i == cntNew[k] )
            {
              /* Cell i is the cell immediately following the last cell on new
              ** sibling page k. If the siblings are not leaf pages of an
              ** intkey b-tree, then cell i is a divider cell.  */
              pNew = apNew[++k];
              if ( 0 == leafData ) continue;
            }
            Debug.Assert( j < nOld );
            Debug.Assert( k < nNew );

            /* If the cell was originally divider cell (and is not now) or
            ** an overflow cell, or if the cell was located on a different sibling
            ** page before the balancing, then the pointer map entries associated
            ** with any child or overflow pages need to be updated.  */
            if ( isDivider != 0 || pOld.pgno != pNew.pgno )
            {
              if ( 0 == leafCorrection )
              {
                ptrmapPut( pBt, sqlite3Get4byte( apCell[i] ), PTRMAP_BTREE, pNew.pgno, ref rc );
              }
              if ( szCell[i] > pNew.minLocal )
              {
                ptrmapPutOvflPtr( pNew, apCell[i], ref rc );
              }
            }
          }

          if ( 0 == leafCorrection )
          {
            for ( i = 0; i < nNew; i++ )
            {
              u32 key = sqlite3Get4byte( apNew[i].aData, 8 );
              ptrmapPut( pBt, key, PTRMAP_BTREE, apNew[i].pgno, ref rc );
            }
          }

#if FALSE
/* The ptrmapCheckPages() contains Debug.Assert() statements that verify that
** all pointer map pages are set correctly. This is helpful while
** debugging. This is usually disabled because a corrupt database may
** cause an Debug.Assert() statement to fail.  */
ptrmapCheckPages(apNew, nNew);
ptrmapCheckPages(pParent, 1);
#endif
        }

      Debug.Assert( pParent.isInit != 0 );
      TRACE( "BALANCE: finished: old=%d new=%d cells=%d\n",
      nOld, nNew, nCell );

    /*
    ** Cleanup before returning.
    */
    balance_cleanup:
      sqlite3ScratchFree( apCell );
      for ( i = 0; i < nOld; i++ )
      {
        releasePage( apOld[i] );
      }
      for ( i = 0; i < nNew; i++ )
      {
        releasePage( apNew[i] );
      }

      return rc;
    }


    /*
    ** This function is called when the root page of a b-tree structure is
    ** overfull (has one or more overflow pages).
    **
    ** A new child page is allocated and the contents of the current root
    ** page, including overflow cells, are copied into the child. The root
    ** page is then overwritten to make it an empty page with the right-child
    ** pointer pointing to the new page.
    **
    ** Before returning, all pointer-map entries corresponding to pages
    ** that the new child-page now contains pointers to are updated. The
    ** entry corresponding to the new right-child pointer of the root
    ** page is also updated.
    **
    ** If successful, ppChild is set to contain a reference to the child
    ** page and SQLITE_OK is returned. In this case the caller is required
    ** to call releasePage() on ppChild exactly once. If an error occurs,
    ** an error code is returned and ppChild is set to 0.
    */
    static int balance_deeper( MemPage pRoot, ref MemPage ppChild )
    {
      int rc;                        /* Return value from subprocedures */
      MemPage pChild = null;           /* Pointer to a new child page */
      Pgno pgnoChild = 0;            /* Page number of the new child page */
      BtShared pBt = pRoot.pBt;    /* The BTree */

      Debug.Assert( pRoot.nOverflow > 0 );
      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );

      /* Make pRoot, the root page of the b-tree, writable. Allocate a new
      ** page that will become the new right-child of pPage. Copy the contents
      ** of the node stored on pRoot into the new child page.
      */
      rc = sqlite3PagerWrite( pRoot.pDbPage );
      if ( rc == SQLITE_OK )
      {
        rc = allocateBtreePage( pBt, ref pChild, ref pgnoChild, pRoot.pgno, 0 );
        copyNodeContent( pRoot, pChild, ref rc );
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
        if ( pBt.autoVacuum )
#else
if (false)
#endif
        {
          ptrmapPut( pBt, pgnoChild, PTRMAP_BTREE, pRoot.pgno, ref rc );
        }
      }
      if ( rc != 0 )
      {
        ppChild = null;
        releasePage( pChild );
        return rc;
      }
      Debug.Assert( sqlite3PagerIswriteable( pChild.pDbPage ) );
      Debug.Assert( sqlite3PagerIswriteable( pRoot.pDbPage ) );
      Debug.Assert( pChild.nCell == pRoot.nCell );

      TRACE( "BALANCE: copy root %d into %d\n", pRoot.pgno, pChild.pgno );

      /* Copy the overflow cells from pRoot to pChild */
      Array.Copy( pRoot.aOvfl, pChild.aOvfl, pRoot.nOverflow );//memcpy(pChild.aOvfl, pRoot.aOvfl, pRoot.nOverflow*sizeof(pRoot.aOvfl[0]));
      pChild.nOverflow = pRoot.nOverflow;

      /* Zero the contents of pRoot. Then install pChild as the right-child. */
      zeroPage( pRoot, pChild.aData[0] & ~PTF_LEAF );
      sqlite3Put4byte( pRoot.aData, pRoot.hdrOffset + 8, pgnoChild );

      ppChild = pChild;
      return SQLITE_OK;
    }

    /*
    ** The page that pCur currently points to has just been modified in
    ** some way. This function figures out if this modification means the
    ** tree needs to be balanced, and if so calls the appropriate balancing
    ** routine. Balancing routines are:
    **
    **   balance_quick()
    **   balance_deeper()
    **   balance_nonroot()
    */
    static u8[] aBalanceQuickSpace = new u8[13];
    static int balance( BtCursor pCur )
    {
      int rc = SQLITE_OK;
      int nMin = pCur.pBt.usableSize * 2 / 3;

      //u8[] pFree = null;

#if !NDEBUG || SQLITE_COVERAGE_TEST || DEBUG
      int balance_quick_called = 0;//TESTONLY( int balance_quick_called = 0 );
      int balance_deeper_called = 0;//TESTONLY( int balance_deeper_called = 0 );
#else
int balance_quick_called = 0;
int balance_deeper_called = 0;
#endif

      do
      {
        int iPage = pCur.iPage;
        MemPage pPage = pCur.apPage[iPage];

        if ( iPage == 0 )
        {
          if ( pPage.nOverflow != 0 )
          {
            /* The root page of the b-tree is overfull. In this case call the
            ** balance_deeper() function to create a new child for the root-page
            ** and copy the current contents of the root-page to it. The
            ** next iteration of the do-loop will balance the child page.
            */
            Debug.Assert( ( balance_deeper_called++ ) == 0 );
            rc = balance_deeper( pPage, ref pCur.apPage[1] );
            if ( rc == SQLITE_OK )
            {
              pCur.iPage = 1;
              pCur.aiIdx[0] = 0;
              pCur.aiIdx[1] = 0;
              Debug.Assert( pCur.apPage[1].nOverflow != 0 );
            }
          }
          else
          {
            break;
          }
        }
        else if ( pPage.nOverflow == 0 && pPage.nFree <= nMin )
        {
          break;
        }
        else
        {
          MemPage pParent = pCur.apPage[iPage - 1];
          int iIdx = pCur.aiIdx[iPage - 1];

          rc = sqlite3PagerWrite( pParent.pDbPage );
          if ( rc == SQLITE_OK )
          {
#if !SQLITE_OMIT_QUICKBALANCE
            if ( pPage.hasData != 0
            && pPage.nOverflow == 1
            && pPage.aOvfl[0].idx == pPage.nCell
            && pParent.pgno != 1
            && pParent.nCell == iIdx
            )
            {
              /* Call balance_quick() to create a new sibling of pPage on which
              ** to store the overflow cell. balance_quick() inserts a new cell
              ** into pParent, which may cause pParent overflow. If this
              ** happens, the next interation of the do-loop will balance pParent
              ** use either balance_nonroot() or balance_deeper(). Until this
              ** happens, the overflow cell is stored in the aBalanceQuickSpace[]
              ** buffer.
              **
              ** The purpose of the following Debug.Assert() is to check that only a
              ** single call to balance_quick() is made for each call to this
              ** function. If this were not verified, a subtle bug involving reuse
              ** of the aBalanceQuickSpace[] might sneak in.
              */
              Debug.Assert( ( balance_quick_called++ ) == 0 );
              rc = balance_quick( pParent, pPage, aBalanceQuickSpace );
            }
            else
#endif
            {
              /* In this case, call balance_nonroot() to redistribute cells
              ** between pPage and up to 2 of its sibling pages. This involves
              ** modifying the contents of pParent, which may cause pParent to
              ** become overfull or underfull. The next iteration of the do-loop
              ** will balance the parent page to correct this.
              **
              ** If the parent page becomes overfull, the overflow cell or cells
              ** are stored in the pSpace buffer allocated immediately below.
              ** A subsequent iteration of the do-loop will deal with this by
              ** calling balance_nonroot() (balance_deeper() may be called first,
              ** but it doesn't deal with overflow cells - just moves them to a
              ** different page). Once this subsequent call to balance_nonroot()
              ** has completed, it is safe to release the pSpace buffer used by
              ** the previous call, as the overflow cell data will have been
              ** copied either into the body of a database page or into the new
              ** pSpace buffer passed to the latter call to balance_nonroot().
              */
              //u8[] pSpace = new u8[pCur.pBt.pageSize];// u8 pSpace = sqlite3PageMalloc( pCur.pBt.pageSize );
              rc = balance_nonroot( pParent, iIdx, null, iPage == 1 ? 1 : 0 );
              //if (pFree != null)
              //{
              //  /* If pFree is not NULL, it points to the pSpace buffer used
              //  ** by a previous call to balance_nonroot(). Its contents are
              //  ** now stored either on real database pages or within the
              //  ** new pSpace buffer, so it may be safely freed here. */
              //  sqlite3PageFree(ref pFree);
              //}

              /* The pSpace buffer will be freed after the next call to
              ** balance_nonroot(), or just before this function returns, whichever
              ** comes first. */
              //pFree = pSpace;
            }
          }

          pPage.nOverflow = 0;

          /* The next iteration of the do-loop balances the parent page. */
          releasePage( pPage );
          pCur.iPage--;
        }
      } while ( rc == SQLITE_OK );

      //if (pFree != null)
      //{
      //  sqlite3PageFree(ref pFree);
      //}
      return rc;
    }


    /*
    ** Insert a new record into the BTree.  The key is given by (pKey,nKey)
    ** and the data is given by (pData,nData).  The cursor is used only to
    ** define what table the record should be inserted into.  The cursor
    ** is left pointing at a random location.
    **
    ** For an INTKEY table, only the nKey value of the key is used.  pKey is
    ** ignored.  For a ZERODATA table, the pData and nData are both ignored.
    **
    ** If the seekResult parameter is non-zero, then a successful call to
    ** MovetoUnpacked() to seek cursor pCur to (pKey, nKey) has already
    ** been performed. seekResult is the search result returned (a negative
    ** number if pCur points at an entry that is smaller than (pKey, nKey), or
    ** a positive value if pCur points at an etry that is larger than
    ** (pKey, nKey)).
    **
    ** If the seekResult parameter is non-zero, then the caller guarantees that
    ** cursor pCur is pointing at the existing copy of a row that is to be
    ** overwritten.  If the seekResult parameter is 0, then cursor pCur may
    ** point to any entry or to no entry at all and so this function has to seek
    ** the cursor before the new key can be inserted.
    */
    static int sqlite3BtreeInsert(
    BtCursor pCur,                /* Insert data into the table of this cursor */
    byte[] pKey, i64 nKey,        /* The key of the new record */
    byte[] pData, int nData,      /* The data of the new record */
    int nZero,                    /* Number of extra 0 bytes to append to data */
    int appendBias,               /* True if this is likely an append */
    int seekResult                /* Result of prior MovetoUnpacked() call */
    )
    {
      int rc;
      int loc = seekResult;       /* -1: before desired location  +1: after */
      int szNew = 0;
      int idx;
      MemPage pPage;
      Btree p = pCur.pBtree;
      BtShared pBt = p.pBt;
      int oldCell;
      byte[] newCell = null;

      if ( pCur.eState == CURSOR_FAULT )
      {
        Debug.Assert( pCur.skipNext != SQLITE_OK );
        return pCur.skipNext;
      }

      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( pCur.wrFlag != 0 && pBt.inTransaction == TRANS_WRITE && !pBt.readOnly );
      Debug.Assert( hasSharedCacheTableLock( p, pCur.pgnoRoot, pCur.pKeyInfo != null ? 1 : 0, 2 ) );

      /* Assert that the caller has been consistent. If this cursor was opened
      ** expecting an index b-tree, then the caller should be inserting blob
      ** keys with no associated data. If the cursor was opened expecting an
      ** intkey table, the caller should be inserting integer keys with a
      ** blob of associated data.  */
      Debug.Assert( ( pKey == null ) == ( pCur.pKeyInfo == null ) );

      /* If this is an insert into a table b-tree, invalidate any incrblob
      ** cursors open on the row being replaced (assuming this is a replace
      ** operation - if it is not, the following is a no-op).  */
      if ( pCur.pKeyInfo == null )
      {
        invalidateIncrblobCursors( p, nKey, 0 );
      }

      /* Save the positions of any other cursors open on this table.
      **
      ** In some cases, the call to btreeMoveto() below is a no-op. For
      ** example, when inserting data into a table with auto-generated integer
      ** keys, the VDBE layer invokes sqlite3BtreeLast() to figure out the
      ** integer key to use. It then calls this function to actually insert the
      ** data into the intkey B-Tree. In this case btreeMoveto() recognizes
      ** that the cursor is already where it needs to be and returns without
      ** doing any work. To avoid thwarting these optimizations, it is important
      ** not to clear the cursor here.
      */
      rc = saveAllCursors( pBt, pCur.pgnoRoot, pCur );
      if ( rc != 0 ) return rc;
      if ( 0 == loc )
      {
        rc = btreeMoveto( pCur, pKey, nKey, appendBias, ref loc );
        if ( rc != 0 ) return rc;
      }
      Debug.Assert( pCur.eState == CURSOR_VALID || ( pCur.eState == CURSOR_INVALID && loc != 0 ) );

      pPage = pCur.apPage[pCur.iPage];
      Debug.Assert( pPage.intKey != 0 || nKey >= 0 );
      Debug.Assert( pPage.leaf != 0 || 0 == pPage.intKey );

      TRACE( "INSERT: table=%d nkey=%lld ndata=%d page=%d %s\n",
      pCur.pgnoRoot, nKey, nData, pPage.pgno,
      loc == 0 ? "overwrite" : "new entry" );
      Debug.Assert( pPage.isInit != 0 );
      allocateTempSpace( pBt );
      newCell = pBt.pTmpSpace;
      //if (newCell == null) return SQLITE_NOMEM;
      rc = fillInCell( pPage, newCell, pKey, nKey, pData, nData, nZero, ref szNew );
      if ( rc != 0 ) goto end_insert;
      Debug.Assert( szNew == cellSizePtr( pPage, newCell ) );
      Debug.Assert( szNew <= MX_CELL_SIZE( pBt ) );
      idx = pCur.aiIdx[pCur.iPage];
      if ( loc == 0 )
      {
        u16 szOld;
        Debug.Assert( idx < pPage.nCell );
        rc = sqlite3PagerWrite( pPage.pDbPage );
        if ( rc != 0 )
        {
          goto end_insert;
        }
        oldCell = findCell( pPage, idx );
        if ( 0 == pPage.leaf )
        {
          //memcpy(newCell, oldCell, 4);
          newCell[0] = pPage.aData[oldCell + 0];
          newCell[1] = pPage.aData[oldCell + 1];
          newCell[2] = pPage.aData[oldCell + 2];
          newCell[3] = pPage.aData[oldCell + 3];
        }
        szOld = cellSizePtr( pPage, oldCell );
        rc = clearCell( pPage, oldCell );
        dropCell( pPage, idx, szOld, ref rc );
        if ( rc != 0 ) goto end_insert;
      }
      else if ( loc < 0 && pPage.nCell > 0 )
      {
        Debug.Assert( pPage.leaf != 0 );
        idx = ++pCur.aiIdx[pCur.iPage];
      }
      else
      {
        Debug.Assert( pPage.leaf != 0 );
      }
      insertCell( pPage, idx, newCell, szNew, null, 0, ref rc );
      Debug.Assert( rc != SQLITE_OK || pPage.nCell > 0 || pPage.nOverflow > 0 );

      /* If no error has occured and pPage has an overflow cell, call balance()
      ** to redistribute the cells within the tree. Since balance() may move
      ** the cursor, zero the BtCursor.info.nSize and BtCursor.validNKey
      ** variables.
      **
      ** Previous versions of SQLite called moveToRoot() to move the cursor
      ** back to the root page as balance() used to invalidate the contents
      ** of BtCursor.apPage[] and BtCursor.aiIdx[]. Instead of doing that,
      ** set the cursor state to "invalid". This makes common insert operations
      ** slightly faster.
      **
      ** There is a subtle but important optimization here too. When inserting
      ** multiple records into an intkey b-tree using a single cursor (as can
      ** happen while processing an "INSERT INTO ... SELECT" statement), it
      ** is advantageous to leave the cursor pointing to the last entry in
      ** the b-tree if possible. If the cursor is left pointing to the last
      ** entry in the table, and the next row inserted has an integer key
      ** larger than the largest existing key, it is possible to insert the
      ** row without seeking the cursor. This can be a big performance boost.
      */
      pCur.info.nSize = 0;
      pCur.validNKey = false;
      if ( rc == SQLITE_OK && pPage.nOverflow != 0 )
      {
        rc = balance( pCur );

        /* Must make sure nOverflow is reset to zero even if the balance()
        ** fails. Internal data structure corruption will result otherwise.
        ** Also, set the cursor state to invalid. This stops saveCursorPosition()
        ** from trying to save the current position of the cursor.  */
        pCur.apPage[pCur.iPage].nOverflow = 0;
        pCur.eState = CURSOR_INVALID;
      }
      Debug.Assert( pCur.apPage[pCur.iPage].nOverflow == 0 );

    end_insert:
      return rc;
    }

    /*
    ** Delete the entry that the cursor is pointing to.  The cursor
    ** is left pointing at a arbitrary location.
    */
    static int sqlite3BtreeDelete( BtCursor pCur )
    {
      Btree p = pCur.pBtree;
      BtShared pBt = p.pBt;
      int rc;                             /* Return code */
      MemPage pPage;                      /* Page to delete cell from */
      int pCell;                          /* Pointer to cell to delete */
      int iCellIdx;                       /* Index of cell to delete */
      int iCellDepth;                     /* Depth of node containing pCell */

      Debug.Assert( cursorHoldsMutex( pCur ) );
      Debug.Assert( pBt.inTransaction == TRANS_WRITE );
      Debug.Assert( !pBt.readOnly );
      Debug.Assert( pCur.wrFlag != 0 );
      Debug.Assert( hasSharedCacheTableLock( p, pCur.pgnoRoot, pCur.pKeyInfo != null ? 1 : 0, 2 ) );
      Debug.Assert( !hasReadConflicts( p, pCur.pgnoRoot ) );

      if ( NEVER( pCur.aiIdx[pCur.iPage] >= pCur.apPage[pCur.iPage].nCell )
      || NEVER( pCur.eState != CURSOR_VALID )
      )
      {
        return SQLITE_ERROR;  /* Something has gone awry. */
      }

      /* If this is a delete operation to remove a row from a table b-tree,
      ** invalidate any incrblob cursors open on the row being deleted.  */
      if ( pCur.pKeyInfo == null )
      {
        invalidateIncrblobCursors( p, pCur.info.nKey, 0 );
      }

      iCellDepth = pCur.iPage;
      iCellIdx = pCur.aiIdx[iCellDepth];
      pPage = pCur.apPage[iCellDepth];
      pCell = findCell( pPage, iCellIdx );

      /* If the page containing the entry to delete is not a leaf page, move
      ** the cursor to the largest entry in the tree that is smaller than
      ** the entry being deleted. This cell will replace the cell being deleted
      ** from the internal node. The 'previous' entry is used for this instead
      ** of the 'next' entry, as the previous entry is always a part of the
      ** sub-tree headed by the child page of the cell being deleted. This makes
      ** balancing the tree following the delete operation easier.  */
      if ( 0 == pPage.leaf )
      {
        int notUsed = 0;
        rc = sqlite3BtreePrevious( pCur, ref notUsed );
        if ( rc != 0 ) return rc;
      }

      /* Save the positions of any other cursors open on this table before
      ** making any modifications. Make the page containing the entry to be
      ** deleted writable. Then free any overflow pages associated with the
      ** entry and finally remove the cell itself from within the page.
      */
      rc = saveAllCursors( pBt, pCur.pgnoRoot, pCur );
      if ( rc != 0 ) return rc;
      rc = sqlite3PagerWrite( pPage.pDbPage );
      if ( rc != 0 ) return rc;
      rc = clearCell( pPage, pCell );
      dropCell( pPage, iCellIdx, cellSizePtr( pPage, pCell ), ref rc );
      if ( rc != 0 ) return rc;

      /* If the cell deleted was not located on a leaf page, then the cursor
      ** is currently pointing to the largest entry in the sub-tree headed
      ** by the child-page of the cell that was just deleted from an internal
      ** node. The cell from the leaf node needs to be moved to the internal
      ** node to replace the deleted cell.  */
      if ( 0 == pPage.leaf )
      {
        MemPage pLeaf = pCur.apPage[pCur.iPage];
        int nCell;
        Pgno n = pCur.apPage[iCellDepth + 1].pgno;
        //byte[] pTmp;

        pCell = findCell( pLeaf, pLeaf.nCell - 1 );
        nCell = cellSizePtr( pLeaf, pCell );
        Debug.Assert( MX_CELL_SIZE( pBt ) >= nCell );

        //allocateTempSpace(pBt);
        //pTmp = pBt.pTmpSpace;

        rc = sqlite3PagerWrite( pLeaf.pDbPage );
        byte[] pNext_4 = sqlite3Malloc(nCell + 4);
        Buffer.BlockCopy( pLeaf.aData, pCell - 4, pNext_4, 0, nCell + 4 );
        insertCell( pPage, iCellIdx, pNext_4, nCell + 4, null, n, ref rc ); //insertCell( pPage, iCellIdx, pCell - 4, nCell + 4, pTmp, n, ref rc );
        dropCell( pLeaf, pLeaf.nCell - 1, nCell, ref rc );
        if ( rc != 0 ) return rc;
      }

      /* Balance the tree. If the entry deleted was located on a leaf page,
      ** then the cursor still points to that page. In this case the first
      ** call to balance() repairs the tree, and the if(...) condition is
      ** never true.
      **
      ** Otherwise, if the entry deleted was on an internal node page, then
      ** pCur is pointing to the leaf page from which a cell was removed to
      ** replace the cell deleted from the internal node. This is slightly
      ** tricky as the leaf node may be underfull, and the internal node may
      ** be either under or overfull. In this case run the balancing algorithm
      ** on the leaf node first. If the balance proceeds far enough up the
      ** tree that we can be sure that any problem in the internal node has
      ** been corrected, so be it. Otherwise, after balancing the leaf node,
      ** walk the cursor up the tree to the internal node and balance it as
      ** well.  */
      rc = balance( pCur );
      if ( rc == SQLITE_OK && pCur.iPage > iCellDepth )
      {
        while ( pCur.iPage > iCellDepth )
        {
          releasePage( pCur.apPage[pCur.iPage--] );
        }
        rc = balance( pCur );
      }

      if ( rc == SQLITE_OK )
      {
        moveToRoot( pCur );
      }
      return rc;
    }

    /*
    ** Create a new BTree table.  Write into piTable the page
    ** number for the root page of the new table.
    **
    ** The type of type is determined by the flags parameter.  Only the
    ** following values of flags are currently in use.  Other values for
    ** flags might not work:
    **
    **     BTREE_INTKEY|BTREE_LEAFDATA     Used for SQL tables with rowid keys
    **     BTREE_ZERODATA                  Used for SQL indices
    */
    static int btreeCreateTable( Btree p, ref int piTable, int flags )
    {
      BtShared pBt = p.pBt;
      MemPage pRoot = new MemPage();
      Pgno pgnoRoot = 0;
      int rc;

      Debug.Assert( sqlite3BtreeHoldsMutex( p ) );
      Debug.Assert( pBt.inTransaction == TRANS_WRITE );
      Debug.Assert( !pBt.readOnly );

#if SQLITE_OMIT_AUTOVACUUM
rc = allocateBtreePage(pBt, ref pRoot, ref pgnoRoot, 1, 0);
if( rc !=0){
return rc;
}
#else
      if ( pBt.autoVacuum )
      {
        Pgno pgnoMove = 0;                    /* Move a page here to make room for the root-page */
        MemPage pPageMove = new MemPage();  /* The page to move to. */

        /* Creating a new table may probably require moving an existing database
        ** to make room for the new tables root page. In case this page turns
        ** out to be an overflow page, delete all overflow page-map caches
        ** held by open cursors.
        */
        invalidateAllOverflowCache( pBt );

        /* Read the value of meta[3] from the database to determine where the
        ** root page of the new table should go. meta[3] is the largest root-page
        ** created so far, so the new root-page is (meta[3]+1).
        */
        sqlite3BtreeGetMeta( p, BTREE_LARGEST_ROOT_PAGE, ref pgnoRoot );
        pgnoRoot++;

        /* The new root-page may not be allocated on a pointer-map page, or the
        ** PENDING_BYTE page.
        */
        while ( pgnoRoot == PTRMAP_PAGENO( pBt, pgnoRoot ) ||
        pgnoRoot == PENDING_BYTE_PAGE( pBt ) )
        {
          pgnoRoot++;
        }
        Debug.Assert( pgnoRoot >= 3 );

        /* Allocate a page. The page that currently resides at pgnoRoot will
        ** be moved to the allocated page (unless the allocated page happens
        ** to reside at pgnoRoot).
        */
        rc = allocateBtreePage( pBt, ref pPageMove, ref pgnoMove, pgnoRoot, 1 );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }

        if ( pgnoMove != pgnoRoot )
        {
          /* pgnoRoot is the page that will be used for the root-page of
          ** the new table (assuming an error did not occur). But we were
          ** allocated pgnoMove. If required (i.e. if it was not allocated
          ** by extending the file), the current page at position pgnoMove
          ** is already journaled.
          */
          u8 eType = 0;
          Pgno iPtrPage = 0;

          releasePage( pPageMove );

          /* Move the page currently at pgnoRoot to pgnoMove. */
          rc = btreeGetPage( pBt, pgnoRoot, ref pRoot, 0 );
          if ( rc != SQLITE_OK )
          {
            return rc;
          }
          rc = ptrmapGet( pBt, pgnoRoot, ref eType, ref iPtrPage );
          if ( eType == PTRMAP_ROOTPAGE || eType == PTRMAP_FREEPAGE )
          {
            rc = SQLITE_CORRUPT_BKPT();
          }
          if ( rc != SQLITE_OK )
          {
            releasePage( pRoot );
            return rc;
          }
          Debug.Assert( eType != PTRMAP_ROOTPAGE );
          Debug.Assert( eType != PTRMAP_FREEPAGE );
          rc = relocatePage( pBt, pRoot, eType, iPtrPage, pgnoMove, 0 );
          releasePage( pRoot );

          /* Obtain the page at pgnoRoot */
          if ( rc != SQLITE_OK )
          {
            return rc;
          }
          rc = btreeGetPage( pBt, pgnoRoot, ref pRoot, 0 );
          if ( rc != SQLITE_OK )
          {
            return rc;
          }
          rc = sqlite3PagerWrite( pRoot.pDbPage );
          if ( rc != SQLITE_OK )
          {
            releasePage( pRoot );
            return rc;
          }
        }
        else
        {
          pRoot = pPageMove;
        }

        /* Update the pointer-map and meta-data with the new root-page number. */
        ptrmapPut( pBt, pgnoRoot, PTRMAP_ROOTPAGE, 0, ref rc );
        if ( rc != 0 )
        {
          releasePage( pRoot );
          return rc;
        }
        rc = sqlite3BtreeUpdateMeta( p, 4, pgnoRoot );
        if ( rc != 0 )
        {
          releasePage( pRoot );
          return rc;
        }

      }
      else
      {
        rc = allocateBtreePage( pBt, ref pRoot, ref pgnoRoot, 1, 0 );
        if ( rc != 0 ) return rc;
      }
#endif
      Debug.Assert( sqlite3PagerIswriteable( pRoot.pDbPage ) );
      zeroPage( pRoot, flags | PTF_LEAF );
      sqlite3PagerUnref( pRoot.pDbPage );
      piTable = (int)pgnoRoot;
      return SQLITE_OK;
    }
    static int sqlite3BtreeCreateTable( Btree p, ref int piTable, int flags )
    {
      int rc;
      sqlite3BtreeEnter( p );
      rc = btreeCreateTable( p, ref piTable, flags );
      sqlite3BtreeLeave( p );
      return rc;
    }

    /*
    ** Erase the given database page and all its children.  Return
    ** the page to the freelist.
    */
    static int clearDatabasePage(
    BtShared pBt,         /* The BTree that contains the table */
    Pgno pgno,            /* Page number to clear */
    int freePageFlag,     /* Deallocate page if true */
    ref int pnChange      /* Add number of Cells freed to this counter */
    )
    {
      MemPage pPage = new MemPage();
      int rc;
      byte[] pCell;
      int i;

      Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
      if ( pgno > pagerPagecount( pBt ) )
      {
        return SQLITE_CORRUPT_BKPT();
      }

      rc = getAndInitPage( pBt, pgno, ref pPage );
      if ( rc != 0 ) return rc;
      for ( i = 0; i < pPage.nCell; i++ )
      {
        int iCell = findCell( pPage, i ); pCell = pPage.aData; //        pCell = findCell( pPage, i );
        if ( 0 == pPage.leaf )
        {
          rc = clearDatabasePage( pBt, sqlite3Get4byte( pCell, iCell ), 1, ref pnChange );
          if ( rc != 0 ) goto cleardatabasepage_out;
        }
        rc = clearCell( pPage, iCell );
        if ( rc != 0 ) goto cleardatabasepage_out;
      }
      if ( 0 == pPage.leaf )
      {
        rc = clearDatabasePage( pBt, sqlite3Get4byte( pPage.aData, 8 ), 1, ref pnChange );
        if ( rc != 0 ) goto cleardatabasepage_out;
      }
      else //if (pnChange != 0)
      {
        //Debug.Assert(pPage.intKey != 0);
        pnChange += pPage.nCell;
      }
      if ( freePageFlag != 0 )
      {
        freePage( pPage, ref rc );
      }
      else if ( ( rc = sqlite3PagerWrite( pPage.pDbPage ) ) == 0 )
      {
        zeroPage( pPage, pPage.aData[0] | PTF_LEAF );
      }

    cleardatabasepage_out:
      releasePage( pPage );
      return rc;
    }

    /*
    ** Delete all information from a single table in the database.  iTable is
    ** the page number of the root of the table.  After this routine returns,
    ** the root page is empty, but still exists.
    **
    ** This routine will fail with SQLITE_LOCKED if there are any open
    ** read cursors on the table.  Open write cursors are moved to the
    ** root of the table.
    **
    ** If pnChange is not NULL, then table iTable must be an intkey table. The
    ** integer value pointed to by pnChange is incremented by the number of
    ** entries in the table.
    */
    static int sqlite3BtreeClearTable( Btree p, int iTable, ref int pnChange )
    {
      int rc;
      BtShared pBt = p.pBt;
      sqlite3BtreeEnter( p );
      Debug.Assert( p.inTrans == TRANS_WRITE );

      /* Invalidate all incrblob cursors open on table iTable (assuming iTable
      ** is the root of a table b-tree - if it is not, the following call is
      ** a no-op).  */
      invalidateIncrblobCursors( p, 0, 1 );

      rc = saveAllCursors( pBt, (Pgno)iTable, null );
      if ( SQLITE_OK == rc )
      {
        rc = clearDatabasePage( pBt, (Pgno)iTable, 0, ref pnChange );
      }
      sqlite3BtreeLeave( p );
      return rc;
    }

    /*
    ** Erase all information in a table and add the root of the table to
    ** the freelist.  Except, the root of the principle table (the one on
    ** page 1) is never added to the freelist.
    **
    ** This routine will fail with SQLITE_LOCKED if there are any open
    ** cursors on the table.
    **
    ** If AUTOVACUUM is enabled and the page at iTable is not the last
    ** root page in the database file, then the last root page
    ** in the database file is moved into the slot formerly occupied by
    ** iTable and that last slot formerly occupied by the last root page
    ** is added to the freelist instead of iTable.  In this say, all
    ** root pages are kept at the beginning of the database file, which
    ** is necessary for AUTOVACUUM to work right.  piMoved is set to the
    ** page number that used to be the last root page in the file before
    ** the move.  If no page gets moved, piMoved is set to 0.
    ** The last root page is recorded in meta[3] and the value of
    ** meta[3] is updated by this procedure.
    */
    static int btreeDropTable( Btree p, Pgno iTable, ref int piMoved )
    {
      int rc;
      MemPage pPage = null;
      BtShared pBt = p.pBt;

      Debug.Assert( sqlite3BtreeHoldsMutex( p ) );
      Debug.Assert( p.inTrans == TRANS_WRITE );

      /* It is illegal to drop a table if any cursors are open on the
      ** database. This is because in auto-vacuum mode the backend may
      ** need to move another root-page to fill a gap left by the deleted
      ** root page. If an open cursor was using this page a problem would
      ** occur.
      **
      ** This error is caught long before control reaches this point.
      */
      if ( NEVER( pBt.pCursor ) )
      {
        sqlite3ConnectionBlocked( p.db, pBt.pCursor.pBtree.db );
        return SQLITE_LOCKED_SHAREDCACHE;
      }

      rc = btreeGetPage( pBt, (Pgno)iTable, ref pPage, 0 );
      if ( rc != 0 ) return rc;
      int Dummy0 = 0; rc = sqlite3BtreeClearTable( p, (int)iTable, ref Dummy0 );
      if ( rc != 0 )
      {
        releasePage( pPage );
        return rc;
      }

      piMoved = 0;

      if ( iTable > 1 )
      {
#if SQLITE_OMIT_AUTOVACUUM
freePage(pPage, ref rc);
releasePage(pPage);
#else
        if ( pBt.autoVacuum )
        {
          Pgno maxRootPgno = 0;
          sqlite3BtreeGetMeta( p, BTREE_LARGEST_ROOT_PAGE, ref maxRootPgno );

          if ( iTable == maxRootPgno )
          {
            /* If the table being dropped is the table with the largest root-page
            ** number in the database, put the root page on the free list.
            */
            freePage( pPage, ref rc );
            releasePage( pPage );
            if ( rc != SQLITE_OK )
            {
              return rc;
            }
          }
          else
          {
            /* The table being dropped does not have the largest root-page
            ** number in the database. So move the page that does into the
            ** gap left by the deleted root-page.
            */
            MemPage pMove = new MemPage();
            releasePage( pPage );
            rc = btreeGetPage( pBt, maxRootPgno, ref pMove, 0 );
            if ( rc != SQLITE_OK )
            {
              return rc;
            }
            rc = relocatePage( pBt, pMove, PTRMAP_ROOTPAGE, 0, iTable, 0 );
            releasePage( pMove );
            if ( rc != SQLITE_OK )
            {
              return rc;
            }
            pMove = null;
            rc = btreeGetPage( pBt, maxRootPgno, ref pMove, 0 );
            freePage( pMove, ref rc );
            releasePage( pMove );
            if ( rc != SQLITE_OK )
            {
              return rc;
            }
            piMoved = (int)maxRootPgno;
          }

          /* Set the new 'max-root-page' value in the database header. This
          ** is the old value less one, less one more if that happens to
          ** be a root-page number, less one again if that is the
          ** PENDING_BYTE_PAGE.
          */
          maxRootPgno--;
          while ( maxRootPgno == PENDING_BYTE_PAGE( pBt )
          || PTRMAP_ISPAGE( pBt, maxRootPgno ) )
          {
            maxRootPgno--;
          }
          Debug.Assert( maxRootPgno != PENDING_BYTE_PAGE( pBt ) );

          rc = sqlite3BtreeUpdateMeta( p, 4, maxRootPgno );
        }
        else
        {
          freePage( pPage, ref rc );
          releasePage( pPage );
        }
#endif
      }
      else
      {
        /* If sqlite3BtreeDropTable was called on page 1.
        ** This really never should happen except in a corrupt
        ** database.
        */
        zeroPage( pPage, PTF_INTKEY | PTF_LEAF );
        releasePage( pPage );
      }
      return rc;
    }
    static int sqlite3BtreeDropTable( Btree p, int iTable, ref int piMoved )
    {
      int rc;
      sqlite3BtreeEnter( p );
      rc = btreeDropTable( p, (u32)iTable, ref piMoved );
      sqlite3BtreeLeave( p );
      return rc;
    }


    /*
    ** This function may only be called if the b-tree connection already
    ** has a read or write transaction open on the database.
    **
    ** Read the meta-information out of a database file.  Meta[0]
    ** is the number of free pages currently in the database.  Meta[1]
    ** through meta[15] are available for use by higher layers.  Meta[0]
    ** is read-only, the others are read/write.
    **
    ** The schema layer numbers meta values differently.  At the schema
    ** layer (and the SetCookie and ReadCookie opcodes) the number of
    ** free pages is not visible.  So Cookie[0] is the same as Meta[1].
    */
    static void sqlite3BtreeGetMeta( Btree p, int idx, ref u32 pMeta )
    {
      BtShared pBt = p.pBt;

      sqlite3BtreeEnter( p );
      Debug.Assert( p.inTrans > TRANS_NONE );
      Debug.Assert( SQLITE_OK == querySharedCacheTableLock( p, MASTER_ROOT, READ_LOCK ) );
      Debug.Assert( pBt.pPage1 != null );
      Debug.Assert( idx >= 0 && idx <= 15 );

      pMeta = sqlite3Get4byte( pBt.pPage1.aData, 36 + idx * 4 );

      /* If auto-vacuum is disabled in this build and this is an auto-vacuum
      ** database, mark the database as read-only.  */
#if SQLITE_OMIT_AUTOVACUUM
if( idx==BTREE_LARGEST_ROOT_PAGE && pMeta>0 ) pBt.readOnly = 1;
#endif

      sqlite3BtreeLeave( p );
    }

    /*
    ** Write meta-information back into the database.  Meta[0] is
    ** read-only and may not be written.
    */
    static int sqlite3BtreeUpdateMeta( Btree p, int idx, u32 iMeta )
    {
      BtShared pBt = p.pBt;
      byte[] pP1;
      int rc;
      Debug.Assert( idx >= 1 && idx <= 15 );
      sqlite3BtreeEnter( p );
      Debug.Assert( p.inTrans == TRANS_WRITE );
      Debug.Assert( pBt.pPage1 != null );
      pP1 = pBt.pPage1.aData;
      rc = sqlite3PagerWrite( pBt.pPage1.pDbPage );
      if ( rc == SQLITE_OK )
      {
        sqlite3Put4byte( pP1, 36 + idx * 4, iMeta );
#if !SQLITE_OMIT_AUTOVACUUM
        if ( idx == BTREE_INCR_VACUUM )
        {
          Debug.Assert( pBt.autoVacuum || iMeta == 0 );
          Debug.Assert( iMeta == 0 || iMeta == 1 );
          pBt.incrVacuum = iMeta != 0;
        }
#endif
      }
      sqlite3BtreeLeave( p );
      return rc;
    }

#if !SQLITE_OMIT_BTREECOUNT
    /*
** The first argument, pCur, is a cursor opened on some b-tree. Count the
** number of entries in the b-tree and write the result to pnEntry.
**
** SQLITE_OK is returned if the operation is successfully executed.
** Otherwise, if an error is encountered (i.e. an IO error or database
** corruption) an SQLite error code is returned.
*/
    static int sqlite3BtreeCount( BtCursor pCur, ref i64 pnEntry )
    {
      i64 nEntry = 0;                      /* Value to return in pnEntry */
      int rc;                              /* Return code */
      rc = moveToRoot( pCur );

      /* Unless an error occurs, the following loop runs one iteration for each
      ** page in the B-Tree structure (not including overflow pages).
      */
      while ( rc == SQLITE_OK )
      {
        int iIdx;                          /* Index of child node in parent */
        MemPage pPage;                    /* Current page of the b-tree */

        /* If this is a leaf page or the tree is not an int-key tree, then
        ** this page contains countable entries. Increment the entry counter
        ** accordingly.
        */
        pPage = pCur.apPage[pCur.iPage];
        if ( pPage.leaf != 0 || 0 == pPage.intKey )
        {
          nEntry += pPage.nCell;
        }

        /* pPage is a leaf node. This loop navigates the cursor so that it
        ** points to the first interior cell that it points to the parent of
        ** the next page in the tree that has not yet been visited. The
        ** pCur.aiIdx[pCur.iPage] value is set to the index of the parent cell
        ** of the page, or to the number of cells in the page if the next page
        ** to visit is the right-child of its parent.
        **
        ** If all pages in the tree have been visited, return SQLITE_OK to the
        ** caller.
        */
        if ( pPage.leaf != 0 )
        {
          do
          {
            if ( pCur.iPage == 0 )
            {
              /* All pages of the b-tree have been visited. Return successfully. */
              pnEntry = nEntry;
              return SQLITE_OK;
            }
            moveToParent( pCur );
          } while ( pCur.aiIdx[pCur.iPage] >= pCur.apPage[pCur.iPage].nCell );

          pCur.aiIdx[pCur.iPage]++;
          pPage = pCur.apPage[pCur.iPage];
        }

        /* Descend to the child node of the cell that the cursor currently
        ** points at. This is the right-child if (iIdx==pPage.nCell).
        */
        iIdx = pCur.aiIdx[pCur.iPage];
        if ( iIdx == pPage.nCell )
        {
          rc = moveToChild( pCur, sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 ) );
        }
        else
        {
          rc = moveToChild( pCur, sqlite3Get4byte( pPage.aData, findCell( pPage, iIdx ) ) );
        }
      }

      /* An error has occurred. Return an error code. */
      return rc;
    }
#endif

    /*
** Return the pager associated with a BTree.  This routine is used for
** testing and debugging only.
*/
    static Pager sqlite3BtreePager( Btree p )
    {
      return p.pBt.pPager;
    }

#if !SQLITE_OMIT_INTEGRITY_CHECK
    /*
** Append a message to the error message string.
*/
    static void checkAppendMsg(
    IntegrityCk pCheck,
    string zMsg1,
    string zFormat,
    params object[] ap
    )
    {
      //va_list ap;
      if ( 0 == pCheck.mxErr ) return;
      pCheck.mxErr--;
      pCheck.nErr++;
      va_start( ap, zFormat );
      if ( pCheck.errMsg.zText.Length != 0 )
      {
        sqlite3StrAccumAppend( pCheck.errMsg, "\n", 1 );
      }
      if ( !string.IsNullOrEmpty( zMsg1 ) )
      {
        sqlite3StrAccumAppend( pCheck.errMsg, zMsg1, -1 );
      }
      sqlite3VXPrintf( pCheck.errMsg, 1, zFormat, ap );
      va_end( ap );
      //if( pCheck.errMsg.mallocFailed ){
      //  pCheck.mallocFailed = 1;
      //}
    }
#endif //* SQLITE_OMIT_INTEGRITY_CHECK */

#if !SQLITE_OMIT_INTEGRITY_CHECK
    /*
** Add 1 to the reference count for page iPage.  If this is the second
** reference to the page, add an error message to pCheck.zErrMsg.
** Return 1 if there are 2 ore more references to the page and 0 if
** if this is the first reference to the page.
**
** Also check that the page number is in bounds.
*/
    static int checkRef( IntegrityCk pCheck, Pgno iPage, string zContext )
    {
      if ( iPage == 0 ) return 1;
      if ( iPage > pCheck.nPage )
      {
        checkAppendMsg( pCheck, zContext, "invalid page number %d", iPage );
        return 1;
      }
      if ( pCheck.anRef[iPage] == 1 )
      {
        checkAppendMsg( pCheck, zContext, "2nd reference to page %d", iPage );
        return 1;
      }
      return ( ( pCheck.anRef[iPage]++ ) > 1 ) ? 1 : 0;
    }

#if !SQLITE_OMIT_AUTOVACUUM
    /*
** Check that the entry in the pointer-map for page iChild maps to
** page iParent, pointer type ptrType. If not, append an error message
** to pCheck.
*/
    static void checkPtrmap(
    IntegrityCk pCheck,    /* Integrity check context */
    Pgno iChild,           /* Child page number */
    u8 eType,              /* Expected pointer map type */
    Pgno iParent,          /* Expected pointer map parent page number */
    string zContext        /* Context description (used for error msg) */
    )
    {
      int rc;
      u8 ePtrmapType = 0;
      Pgno iPtrmapParent = 0;

      rc = ptrmapGet( pCheck.pBt, iChild, ref ePtrmapType, ref iPtrmapParent );
      if ( rc != SQLITE_OK )
      {
        //if( rc==SQLITE_NOMEM || rc==SQLITE_IOERR_NOMEM ) pCheck.mallocFailed = 1;
        checkAppendMsg( pCheck, zContext, "Failed to read ptrmap key=%d", iChild );
        return;
      }

      if ( ePtrmapType != eType || iPtrmapParent != iParent )
      {
        checkAppendMsg( pCheck, zContext,
        "Bad ptr map entry key=%d expected=(%d,%d) got=(%d,%d)",
        iChild, eType, iParent, ePtrmapType, iPtrmapParent );
      }
    }
#endif

    /*
** Check the integrity of the freelist or of an overflow page list.
** Verify that the number of pages on the list is N.
*/
    static void checkList(
    IntegrityCk pCheck,  /* Integrity checking context */
    int isFreeList,       /* True for a freelist.  False for overflow page list */
    int iPage,            /* Page number for first page in the list */
    int N,                /* Expected number of pages in the list */
    string zContext        /* Context for error messages */
    )
    {
      int i;
      int expected = N;
      int iFirst = iPage;
      while ( N-- > 0 && pCheck.mxErr != 0 )
      {
        DbPage pOvflPage = new PgHdr();
        byte[] pOvflData;
        if ( iPage < 1 )
        {
          checkAppendMsg( pCheck, zContext,
          "%d of %d pages missing from overflow list starting at %d",
          N + 1, expected, iFirst );
          break;
        }
        if ( checkRef( pCheck, (u32)iPage, zContext ) != 0 ) break;
        if ( sqlite3PagerGet( pCheck.pPager, (Pgno)iPage, ref pOvflPage ) != 0 )
        {
          checkAppendMsg( pCheck, zContext, "failed to get page %d", iPage );
          break;
        }
        pOvflData = sqlite3PagerGetData( pOvflPage );
        if ( isFreeList != 0 )
        {
          int n = (int)sqlite3Get4byte( pOvflData, 4 );
#if !SQLITE_OMIT_AUTOVACUUM
          if ( pCheck.pBt.autoVacuum )
          {
            checkPtrmap( pCheck, (u32)iPage, PTRMAP_FREEPAGE, 0, zContext );
          }
#endif
          if ( n > pCheck.pBt.usableSize / 4 - 2 )
          {
            checkAppendMsg( pCheck, zContext,
            "freelist leaf count too big on page %d", iPage );
            N--;
          }
          else
          {
            for ( i = 0; i < n; i++ )
            {
              Pgno iFreePage = sqlite3Get4byte( pOvflData, 8 + i * 4 );
#if !SQLITE_OMIT_AUTOVACUUM
              if ( pCheck.pBt.autoVacuum )
              {
                checkPtrmap( pCheck, iFreePage, PTRMAP_FREEPAGE, 0, zContext );
              }
#endif
              checkRef( pCheck, iFreePage, zContext );
            }
            N -= n;
          }
        }
#if !SQLITE_OMIT_AUTOVACUUM
        else
        {
          /* If this database supports auto-vacuum and iPage is not the last
          ** page in this overflow list, check that the pointer-map entry for
          ** the following page matches iPage.
          */
          if ( pCheck.pBt.autoVacuum && N > 0 )
          {
            i = (int)sqlite3Get4byte( pOvflData );
            checkPtrmap( pCheck, (u32)i, PTRMAP_OVERFLOW2, (u32)iPage, zContext );
          }
        }
#endif
        iPage = (int)sqlite3Get4byte( pOvflData );
        sqlite3PagerUnref( pOvflPage );
      }
    }
#endif //* SQLITE_OMIT_INTEGRITY_CHECK */

#if !SQLITE_OMIT_INTEGRITY_CHECK
    /*
** Do various sanity checks on a single page of a tree.  Return
** the tree depth.  Root pages return 0.  Parents of root pages
** return 1, and so forth.
**
** These checks are done:
**
**      1.  Make sure that cells and freeblocks do not overlap
**          but combine to completely cover the page.
**  NO  2.  Make sure cell keys are in order.
**  NO  3.  Make sure no key is less than or equal to zLowerBound.
**  NO  4.  Make sure no key is greater than or equal to zUpperBound.
**      5.  Check the integrity of overflow pages.
**      6.  Recursively call checkTreePage on all children.
**      7.  Verify that the depth of all children is the same.
**      8.  Make sure this page is at least 33% full or else it is
**          the root of the tree.
*/

    static i64 refNULL = 0;   //Dummy for C# ref NULL

    static int checkTreePage(
    IntegrityCk pCheck,    /* Context for the sanity check */
    int iPage,             /* Page number of the page to check */
    string zParentContext, /* Parent context */
    ref i64 pnParentMinKey,
    ref i64 pnParentMaxKey,
    object _pnParentMinKey, /* C# Needed to determine if content passed*/
    object _pnParentMaxKey  /* C# Needed to determine if content passed*/
    )
    {
      MemPage pPage = new MemPage();
      int i, rc, depth, d2, pgno, cnt;
      int hdr, cellStart;
      int nCell;
      u8[] data;
      BtShared pBt;
      int usableSize;
      string zContext = "";//[100];
      byte[] hit = null;
      i64 nMinKey = 0;
      i64 nMaxKey = 0;
   

      sqlite3_snprintf( 200, ref zContext, "Page %d: ", iPage );

      /* Check that the page exists
      */
      pBt = pCheck.pBt;
      usableSize = pBt.usableSize;
      if ( iPage == 0 ) return 0;
      if ( checkRef( pCheck, (u32)iPage, zParentContext ) != 0 ) return 0;
      if ( ( rc = btreeGetPage( pBt, (Pgno)iPage, ref pPage, 0 ) ) != 0 )
      {
        checkAppendMsg( pCheck, zContext,
        "unable to get the page. error code=%d", rc );
        return 0;
      }

      /* Clear MemPage.isInit to make sure the corruption detection code in
      ** btreeInitPage() is executed.  */
      pPage.isInit = 0;
      if ( ( rc = btreeInitPage( pPage ) ) != 0 )
      {
        Debug.Assert( rc == SQLITE_CORRUPT );  /* The only possible error from InitPage */
        checkAppendMsg( pCheck, zContext,
        "btreeInitPage() returns error code %d", rc );
        releasePage( pPage );
        return 0;
      }

      /* Check out all the cells.
      */
      depth = 0;
      for ( i = 0; i < pPage.nCell && pCheck.mxErr != 0; i++ )
      {
        u8[] pCell;
        u32 sz;
        CellInfo info = new CellInfo();

        /* Check payload overflow pages
        */
        sqlite3_snprintf( 200, ref zContext,
        "On tree page %d cell %d: ", iPage, i );
        int iCell = findCell( pPage, i ); //pCell = findCell( pPage, i );
        pCell = pPage.aData;
        btreeParseCellPtr( pPage, iCell, ref info ); //btreeParseCellPtr( pPage, pCell, info );
        sz = info.nData;
        if ( 0 == pPage.intKey ) sz += (u32)info.nKey;
        /* For intKey pages, check that the keys are in order.
        */
        else if (i == 0) nMinKey = nMaxKey = info.nKey;
        else
        {
          if (info.nKey <= nMaxKey)
          {
            checkAppendMsg(pCheck, zContext,
                "Rowid %lld out of order (previous was %lld)", info.nKey, nMaxKey);
          }
          nMaxKey = info.nKey;
        }
        Debug.Assert(sz == info.nPayload);
        if ( ( sz > info.nLocal )
          //&& (pCell[info.iOverflow]<=&pPage.aData[pBt.usableSize])
        )
        {
          int nPage = (int)( sz - info.nLocal + usableSize - 5 ) / ( usableSize - 4 );
          Pgno pgnoOvfl = sqlite3Get4byte( pCell, iCell, info.iOverflow );
#if !SQLITE_OMIT_AUTOVACUUM
          if ( pBt.autoVacuum )
          {
            checkPtrmap( pCheck, pgnoOvfl, PTRMAP_OVERFLOW1, (u32)iPage, zContext );
          }
#endif
          checkList( pCheck, 0, (int)pgnoOvfl, nPage, zContext );
        }

        /* Check sanity of left child page.
        */
        if ( 0 == pPage.leaf )
        {
          pgno = (int)sqlite3Get4byte( pCell, iCell ); //sqlite3Get4byte( pCell );
#if !SQLITE_OMIT_AUTOVACUUM
          if ( pBt.autoVacuum )
          {
            checkPtrmap( pCheck, (u32)pgno, PTRMAP_BTREE, (u32)iPage, zContext );
          }
#endif
          if ( i == 0 )
            d2 = checkTreePage( pCheck, pgno, zContext, ref nMinKey, ref refNULL, pCheck, null ); 
          else
            d2 = checkTreePage( pCheck, pgno, zContext, ref nMinKey, ref nMaxKey, pCheck, pCheck );

          if ( i > 0 && d2 != depth )
          {
            checkAppendMsg( pCheck, zContext, "Child page depth differs" );
          }
          depth = d2;
        }
      }
      if ( 0 == pPage.leaf )
      {
        pgno = (int)sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 );
        sqlite3_snprintf( 200, ref zContext,
        "On page %d at right child: ", iPage );
#if !SQLITE_OMIT_AUTOVACUUM
        if ( pBt.autoVacuum )
        {
          checkPtrmap(pCheck, (u32)pgno, PTRMAP_BTREE, (u32)iPage, zContext);
        }
#endif
        //    checkTreePage(pCheck, pgno, zContext, NULL, !pPage->nCell ? NULL : &nMaxKey);
        if ( 0 == pPage.nCell )
          checkTreePage( pCheck, pgno, zContext, ref refNULL, ref refNULL, null, null );
        else
          checkTreePage( pCheck, pgno, zContext, ref refNULL, ref nMaxKey, null, pCheck );
      }

      /* For intKey leaf pages, check that the min/max keys are in order
      ** with any left/parent/right pages.
      */
      if (pPage.leaf != 0 && pPage.intKey != 0)
      {
        /* if we are a left child page */
        if (_pnParentMinKey != null)
        {
          /* if we are the left most child page */
          if (_pnParentMaxKey == null)
          {
            if (nMaxKey > pnParentMinKey)
            {
              checkAppendMsg(pCheck, zContext,
                  "Rowid %lld out of order (max larger than parent min of %lld)",
                  nMaxKey, pnParentMinKey);
            }
          }
          else
          {
            if (nMinKey <= pnParentMinKey)
            {
              checkAppendMsg(pCheck, zContext,
                  "Rowid %lld out of order (min less than parent min of %lld)",
                  nMinKey, pnParentMinKey);
            }
            if (nMaxKey > pnParentMaxKey)
            {
              checkAppendMsg(pCheck, zContext,
                  "Rowid %lld out of order (max larger than parent max of %lld)",
                  nMaxKey, pnParentMaxKey);
            }
            pnParentMinKey = nMaxKey;
          }
          /* else if we're a right child page */
        }
        else if (_pnParentMaxKey!=null)
        {
          if (nMinKey <= pnParentMaxKey)
          {
            checkAppendMsg(pCheck, zContext,
                "Rowid %lld out of order (min less than parent max of %lld)",
                nMinKey, pnParentMaxKey);
          }
        }
      }

      /* Check for complete coverage of the page
      */
      data = pPage.aData;
      hdr = pPage.hdrOffset;
      hit = sqlite3Malloc(pBt.pageSize);
      //if( hit==null ){
      //  pCheck.mallocFailed = 1;
      //}else
      {
        u16 contentOffset = (u16)get2byte( data, hdr + 5 );
        Debug.Assert( contentOffset <= usableSize );  /* Enforced by btreeInitPage() */
        Array.Clear( hit, contentOffset, usableSize - contentOffset );//memset(hit+contentOffset, 0, usableSize-contentOffset);
        for ( int iLoop = contentOffset - 1; iLoop >= 0; iLoop-- ) hit[iLoop] = 1;//memset(hit, 1, contentOffset);
        nCell = get2byte( data, hdr + 3 );
        cellStart = hdr + 12 - 4 * pPage.leaf;
        for ( i = 0; i < nCell; i++ )
        {
          int pc = get2byte( data, cellStart + i * 2 );
          u16 size = 1024;
          int j;
          if ( pc <= usableSize - 4 )
          {
            size = cellSizePtr( pPage, data, pc );
          }
          if ( ( pc + size - 1 ) >= usableSize )
          {
            checkAppendMsg( pCheck, null,
            "Corruption detected in cell %d on page %d", i, iPage);
          }
          else
          {
            for ( j = pc + size - 1; j >= pc; j-- ) hit[j]++;
          }
        }
        i = get2byte( data, hdr + 1 );
        while ( i > 0 )
        {
          int size, j;
          Debug.Assert( i <= usableSize - 4 );     /* Enforced by btreeInitPage() */
          size = get2byte( data, i + 2 );
          Debug.Assert( i + size <= usableSize );  /* Enforced by btreeInitPage() */
          for ( j = i + size - 1; j >= i; j-- ) hit[j]++;
          j = get2byte( data, i );
          Debug.Assert( j == 0 || j > i + size );  /* Enforced by btreeInitPage() */
          Debug.Assert( j <= usableSize - 4 );   /* Enforced by btreeInitPage() */
          i = j;
        }
        for ( i = cnt = 0; i < usableSize; i++ )
        {
          if ( hit[i] == 0 )
          {
            cnt++;
          }
          else if ( hit[i] > 1 )
          {
            checkAppendMsg( pCheck, "",
            "Multiple uses for byte %d of page %d", i, iPage );
            break;
          }
        }
        if ( cnt != data[hdr + 7] )
        {
          checkAppendMsg( pCheck, null,
          "Fragmentation of %d bytes reported as %d on page %d",
          cnt, data[hdr + 7], iPage );
        }
      }
      sqlite3PageFree(ref hit);
      releasePage( pPage );
      return depth + 1;
    }
#endif //* SQLITE_OMIT_INTEGRITY_CHECK */

#if !SQLITE_OMIT_INTEGRITY_CHECK
    /*
** This routine does a complete check of the given BTree file.  aRoot[] is
** an array of pages numbers were each page number is the root page of
** a table.  nRoot is the number of entries in aRoot.
**
** A read-only or read-write transaction must be opened before calling
** this function.
**
** Write the number of error seen in pnErr.  Except for some memory
** allocation errors,  an error message held in memory obtained from
** malloc is returned if pnErr is non-zero.  If pnErr==null then NULL is
** returned.  If a memory allocation error occurs, NULL is returned.
*/
    static string sqlite3BtreeIntegrityCheck(
    Btree p,       /* The btree to be checked */
    int[] aRoot,   /* An array of root pages numbers for individual trees */
    int nRoot,     /* Number of entries in aRoot[] */
    int mxErr,     /* Stop reporting errors after this many */
    ref int pnErr  /* Write number of errors seen to this variable */
    )
    {
      Pgno i;
      int nRef;
      IntegrityCk sCheck = new IntegrityCk();
      BtShared pBt = p.pBt;
      //StringBuilder zErr = new StringBuilder( 100 );//char zErr[100];

      sqlite3BtreeEnter( p );
      Debug.Assert( p.inTrans > TRANS_NONE && pBt.inTransaction > TRANS_NONE );
      nRef = sqlite3PagerRefcount( pBt.pPager );
      sCheck.pBt = pBt;
      sCheck.pPager = pBt.pPager;
      sCheck.nPage = pagerPagecount( sCheck.pBt );
      sCheck.mxErr = mxErr;
      sCheck.nErr = 0;
      //sCheck.mallocFailed = 0;
      pnErr = 0;
      if ( sCheck.nPage == 0 )
      {
        sqlite3BtreeLeave( p );
        return "";
      }
      sCheck.anRef = sqlite3Malloc( sCheck.anRef, (int)sCheck.nPage+1);
      //if( !sCheck.anRef ){
      //  pnErr = 1;
      //  sqlite3BtreeLeave(p);
      //  return 0;
      //}
      // for (i = 0; i <= sCheck.nPage; i++) { sCheck.anRef[i] = 0; }
      i = PENDING_BYTE_PAGE( pBt );
      if ( i <= sCheck.nPage )
      {
        sCheck.anRef[i] = 1;
      }
      sqlite3StrAccumInit( sCheck.errMsg, null, 1000, 20000 );

      /* Check the integrity of the freelist
      */
      checkList( sCheck, 1, (int)sqlite3Get4byte( pBt.pPage1.aData, 32 ),
      (int)sqlite3Get4byte( pBt.pPage1.aData, 36 ), "Main freelist: " );

      /* Check all the tables.
      */
      for ( i = 0; (int)i < nRoot && sCheck.mxErr != 0; i++ )
      {
        if ( aRoot[i] == 0 ) continue;
#if !SQLITE_OMIT_AUTOVACUUM
        if ( pBt.autoVacuum && aRoot[i] > 1 )
        {
          checkPtrmap( sCheck, (u32)aRoot[i], PTRMAP_ROOTPAGE, 0, "" );
        }
#endif
        checkTreePage( sCheck, aRoot[i], "List of tree roots: ", ref refNULL, ref refNULL, null, null ); 
      }

      /* Make sure every page in the file is referenced
      */
      for ( i = 1; i <= sCheck.nPage && sCheck.mxErr != 0; i++ )
      {
#if SQLITE_OMIT_AUTOVACUUM
if( sCheck.anRef[i]==null ){
checkAppendMsg(sCheck, 0, "Page %d is never used", i);
}
#else
        /* If the database supports auto-vacuum, make sure no tables contain
** references to pointer-map pages.
*/
        if ( sCheck.anRef[i] == 0 &&
        ( PTRMAP_PAGENO( pBt, i ) != i || !pBt.autoVacuum ) )
        {
          checkAppendMsg( sCheck, null, "Page %d is never used", i );
        }
        if ( sCheck.anRef[i] != 0 &&
        ( PTRMAP_PAGENO( pBt, i ) == i && pBt.autoVacuum ) )
        {
          checkAppendMsg( sCheck, null, "Pointer map page %d is referenced", i );
        }
#endif
      }

      /* Make sure this analysis did not leave any unref() pages.
      ** This is an internal consistency check; an integrity check
      ** of the integrity check.
      */
      if ( NEVER( nRef != sqlite3PagerRefcount( pBt.pPager ) ) )
      {
        checkAppendMsg( sCheck, null,
        "Outstanding page count goes from %d to %d during this analysis",
        nRef, sqlite3PagerRefcount( pBt.pPager )
        );
      }

      /* Clean  up and report errors.
      */
      sqlite3BtreeLeave( p );
      sCheck.anRef = null;// sqlite3_free( ref sCheck.anRef );
      //if( sCheck.mallocFailed ){
      //  sqlite3StrAccumReset(sCheck.errMsg);
      //  pnErr = sCheck.nErr+1;
      //  return 0;
      //}
      pnErr = sCheck.nErr;
      if ( sCheck.nErr == 0 ) sqlite3StrAccumReset( sCheck.errMsg );
      return sqlite3StrAccumFinish( sCheck.errMsg );
    }
#endif //* SQLITE_OMIT_INTEGRITY_CHECK */

    /*
** Return the full pathname of the underlying database file.
**
** The pager filename is invariant as long as the pager is
** open so it is safe to access without the BtShared mutex.
*/
    static string sqlite3BtreeGetFilename( Btree p )
    {
      Debug.Assert( p.pBt.pPager != null );
      return sqlite3PagerFilename( p.pBt.pPager );
    }

    /*
    ** Return the pathname of the journal file for this database. The return
    ** value of this routine is the same regardless of whether the journal file
    ** has been created or not.
    **
    ** The pager journal filename is invariant as long as the pager is
    ** open so it is safe to access without the BtShared mutex.
    */
    static string sqlite3BtreeGetJournalname( Btree p )
    {
      Debug.Assert( p.pBt.pPager != null );
      return sqlite3PagerJournalname( p.pBt.pPager );
    }

    /*
    ** Return non-zero if a transaction is active.
    */
    static bool sqlite3BtreeIsInTrans( Btree p )
    {
      Debug.Assert( p == null || sqlite3_mutex_held( p.db.mutex ) );
      return ( p != null && ( p.inTrans == TRANS_WRITE ) );
    }

    /*
    ** Return non-zero if a read (or write) transaction is active.
    */
    static bool sqlite3BtreeIsInReadTrans( Btree p )
    {
      Debug.Assert( p != null );
      Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
      return p.inTrans != TRANS_NONE;
    }

    static bool sqlite3BtreeIsInBackup( Btree p )
    {
      Debug.Assert( p != null );
      Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
      return p.nBackup != 0;
    }

    /*
    ** This function returns a pointer to a blob of memory associated with
    ** a single shared-btree. The memory is used by client code for its own
    ** purposes (for example, to store a high-level schema associated with
    ** the shared-btree). The btree layer manages reference counting issues.
    **
    ** The first time this is called on a shared-btree, nBytes bytes of memory
    ** are allocated, zeroed, and returned to the caller. For each subsequent
    ** call the nBytes parameter is ignored and a pointer to the same blob
    ** of memory returned.
    **
    ** If the nBytes parameter is 0 and the blob of memory has not yet been
    ** allocated, a null pointer is returned. If the blob has already been
    ** allocated, it is returned as normal.
    **
    ** Just before the shared-btree is closed, the function passed as the
    ** xFree argument when the memory allocation was made is invoked on the
    ** blob of allocated memory. This function should not call sqlite3_free(ref )
    ** on the memory, the btree layer does that.
    */
    static Schema sqlite3BtreeSchema( Btree p, int nBytes, dxFreeSchema xFree )
    {
      BtShared pBt = p.pBt;
      sqlite3BtreeEnter( p );
      if ( null == pBt.pSchema && nBytes != 0 )
      {
        pBt.pSchema = new Schema();//sqlite3MallocZero(nBytes);
        pBt.xFreeSchema = xFree;
      }
      sqlite3BtreeLeave( p );
      return pBt.pSchema;
    }

    /*
    ** Return SQLITE_LOCKED_SHAREDCACHE if another user of the same shared
    ** btree as the argument handle holds an exclusive lock on the
    ** sqlite_master table. Otherwise SQLITE_OK.
    */
    static int sqlite3BtreeSchemaLocked( Btree p )
    {
      int rc;
      Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
      sqlite3BtreeEnter( p );
      rc = querySharedCacheTableLock( p, MASTER_ROOT, READ_LOCK );
      Debug.Assert( rc == SQLITE_OK || rc == SQLITE_LOCKED_SHAREDCACHE );
      sqlite3BtreeLeave( p );
      return rc;
    }


#if !SQLITE_OMIT_SHARED_CACHE
/*
** Obtain a lock on the table whose root page is iTab.  The
** lock is a write lock if isWritelock is true or a read lock
** if it is false.
*/
int sqlite3BtreeLockTable(Btree p, int iTab, u8 isWriteLock){
int rc = SQLITE_OK;
Debug.Assert( p.inTrans!=TRANS_NONE );
if( p.sharable ){
u8 lockType = READ_LOCK + isWriteLock;
Debug.Assert( READ_LOCK+1==WRITE_LOCK );
Debug.Assert( isWriteLock==null || isWriteLock==1 );

sqlite3BtreeEnter(p);
rc = querySharedCacheTableLock(p, iTab, lockType);
if( rc==SQLITE_OK ){
rc = setSharedCacheTableLock(p, iTab, lockType);
}
sqlite3BtreeLeave(p);
}
return rc;
}
#endif

#if !SQLITE_OMIT_INCRBLOB
/*
** Argument pCsr must be a cursor opened for writing on an
** INTKEY table currently pointing at a valid table entry.
** This function modifies the data stored as part of that entry.
**
** Only the data content may only be modified, it is not possible to
** change the length of the data stored. If this function is called with
** parameters that attempt to write past the end of the existing data,
** no modifications are made and SQLITE_CORRUPT is returned.
*/
int sqlite3BtreePutData(BtCursor pCsr, u32 offset, u32 amt, void *z){
int rc;
Debug.Assert( cursorHoldsMutex(pCsr) );
Debug.Assert( sqlite3_mutex_held(pCsr.pBtree.db.mutex) );
Debug.Assert( pCsr.isIncrblobHandle );

rc = restoreCursorPosition(pCsr);
if( rc!=SQLITE_OK ){
return rc;
}
Debug.Assert( pCsr.eState!=CURSOR_REQUIRESEEK );
if( pCsr.eState!=CURSOR_VALID ){
return SQLITE_ABORT;
}

/* Check some assumptions:
**   (a) the cursor is open for writing,
**   (b) there is a read/write transaction open,
**   (c) the connection holds a write-lock on the table (if required),
**   (d) there are no conflicting read-locks, and
**   (e) the cursor points at a valid row of an intKey table.
*/
if( !pCsr.wrFlag ){
return SQLITE_READONLY;
}
Debug.Assert( !pCsr.pBt.readOnly && pCsr.pBt.inTransaction==TRANS_WRITE );
Debug.Assert( hasSharedCacheTableLock(pCsr.pBtree, pCsr.pgnoRoot, 0, 2) );
Debug.Assert( !hasReadConflicts(pCsr.pBtree, pCsr.pgnoRoot) );
Debug.Assert( pCsr.apPage[pCsr.iPage].intKey );

return accessPayload(pCsr, offset, amt, (byte[] *)z, 1);
}

/*
** Set a flag on this cursor to cache the locations of pages from the
** overflow list for the current row. This is used by cursors opened
** for incremental blob IO only.
**
** This function sets a flag only. The actual page location cache
** (stored in BtCursor.aOverflow[]) is allocated and used by function
** accessPayload() (the worker function for sqlite3BtreeData() and
** sqlite3BtreePutData()).
*/
void sqlite3BtreeCacheOverflow(BtCursor pCur){
Debug.Assert( cursorHoldsMutex(pCur) );
Debug.Assert( sqlite3_mutex_held(pCur.pBtree.db.mutex) );
Debug.Assert(!pCur.isIncrblobHandle);
Debug.Assert(!pCur.aOverflow);
pCur.isIncrblobHandle = 1;
}
#endif

  }
}
